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Series 5000 MOSFET stereo power amplifier - Upgrades


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In January - March 1981 ETI published construction articles for the Series 5000 Mosfet stereo power amplifier, Project 477, designed by David Tilbrook.

Jaycar Electronics had made a complete version of the kit available for only $299 and a "BLACK MONOLITH" version of the kit for $319.

The main difference between the two kits was that the "BLACK MONOLITH" version had Beryllium Oxide washers, heatsink grease and the special driver transistor heatsinks.

Other electronic stores made this kit available on the market as well but for the price and quality of the components at the time the one from Jaycar for me was very attractive.

 

After many years of using a home constructed Dick Smith kit version of the PLAYMASTER Forty Forty, using 2N3055 TO-3 power transistors, it was time to move up to a higher level.

For a brief time the Series 5000 MOSFET stereo power amplifier "BLACK MONOLITH" kit version was now on sale for $299 due to possibly other market place competitors.

The Series 5000 stereo control preamplifier, also designed by David Tilbrook, was appetizingly reduced and advertised in a flyer for only $275 for similar above reasons.

So I purchased and built both kits in 1983, when I was an Electrical Apprentice and never looked back.

From then till now I have maintained these beauties and performed various upgrades along the way.

 

The performance and sound quality of the Power Amp had kept me satisfied for several years until that frightful day in 1995 when yes, it did fail!

Shock, horror, smoke and panic but no more sound, what could have gone wrong with this trusty amp and why? 

Was it the fact that my wife was listening to the Silverchair album Frogstomp or the fact that is was up rather loud...oh no, what about the Altec's?

Phew, luckily the Altec's survived so that was a bonus as anything else is relatively fixable.

A thought crossed my mind back then about the use of 0.22 ohm inductive resistors on the power mosfets, ...hmm?

Well this is going to take some TLC so for now a replacement amp will have to suffice while I take the time to do justice to this beauty.

 

One magnificent thing about this amp is it's ease to work on as both the top lid with sides and the bottom panel is easily removed leaving the PCB's fully accessible.

On close examination both supply rail fuses were blown, a few charred 1/4 watt metal film resistors, charring of the boards under these resistors and nothing else visibly out of the ordinary.

From experience replacing the supply rail fuses won't fix it, replacing charred resistors won't either, fault finding transistors and the real cause could be a long on going process.

Not to forget that the reliability of many semiconductors, the circuit board tracks after the repairs, other components have also been compromised so over time they may fail down the track and I might not be lucky next time if this happens again.

This can cost more in time than what it would cost to purchase two new boards and populate them. (At the time RCS had them for a good price so I bought a pair and a Series 5000 preamp main board for another project....)

Luckily the required parts are relatively cheap, the inductors and heatsinks can be recycled however the Hitachi TO-3 power mosfets are not cheap but mine were still okay. (These mosfets were getting difficult to obtain at the time and are now virtually impossible, wish I stocked up back then...)

 

After taking all of this and more on board I then decided it was time to hand pick all of the components and rebuild the two amplifier 477 modules.

Parts to be recycled such as the inductors, heatsinks, power mosfets as well as every newly bought component was thoroughly examined, tested for tolerance etc. where applicable.
Unfortunately the Beryllium Oxide TO-3 washers for the power mosfets had to be replaced as some of them had cracked into pieces so these were replaced with silicon types.

While I was at it I may as well replace the 0.22 ohm resistors with non inductive types to be sure and upgrade whatever capacitors, input and output jacks, etc just for the sake of it.

Acquiring all of the parts took longer than the rebuild of the amplifier modules but this was well worth it as the boards are a through hole design, easy, soldered and done.

Powering up and set up of the bias current in the output stage as per kit instructions (which I had preserved in a folder, yes you guessed it) was a breeze and went without any problems.

 

You would think that all was good by this stage and it might have been, but, I wanted more out of this amp now.

Yes, I was getting picky and looking at better performance such as less hum and to get rid of that dreaded hissssss!

It was like this before, but now, I had to get rid of it once and for all, and why not after coming this far.

So maybe add some bypass capacitors across the main power electrolytics might do the trick, it did reduce the hiss slightly, but it still had hum.

Even worse the transformers were making noise on standby even without the speakers connected, more issues!

Replace the twisted pair on the input jacks with quality screened cable, still had hum issues.

 

The pictures below were taken around this time after the first upgrades. (1995 ish)

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I accepted these issues for some time and then it was decided that one day I may have to rebuild or redesign the general layout of this amplifier, maybe two mono block channels in a single case perhaps.

This then led to the first major power supply up grade using bigger power supply electrolytics, individual bridge rectifiers and Toroidal transformers to hopefully get rid of the transformer hum as well.

To do this I had to re-fabricate the rear panel out of steel (not the best material) but had to be strong to hold the extra weight and stresses associated with a cantilever application.

 

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From the above pictures it can be seen there were some design issues that were also overlooked such as the routing of the input wiring being too close to the Toroidal transformers.

Input and output wiring was also too close together for my liking and mains wiring was still a problem.

The main problem that led to a total failed attempt was that the Toroidal transformers were now noisier than the old EI type transformers that were initially supplied in the kit.

So I then placed each of the EI type transformers on the bench with power applied via an isolation transformer and RCD (only do this if you are a qualified technician as it can be extremely dangerous) and then proceeded to place wedges made from cable tie stubs strategically in between the iron core and the copper hum strap around the transformer winding.

This actually worked and the transformers no longer make any hum or noise even when the off-peak hot water heater signals are injected into the mains late in the evenings. Transformer problem fixed!

Now with this sorted it made sense to do a second power supply upgrade and keep as much as the original kit as this is what the Series 5000 was all about.

The lovely front heatsink and easy to work on case, Hitachi power mosfets, EI core transformers and not to forget the good specifications and circuit design.

It all then led to the final upgrade and layout decisions.

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Some of the main considerations that were made:

Segregation to the mains power supply wiring between the power transformers.

Aluminium segregation between the power supply and the amplifier modules.

Total separation between input and output wiring.

Twisted pair for all AC wiring.

Snubber capacitors across each rectifier diode.

Bypass capacitors across the main electrolytic capacitors.

Added mains suppression capacitor to the IEC connector with fuse and power switch.

ELNA Cerafine electrolytic capacitors for coupling.

Low ESR electrolytic capacitors for power supply applications on the amplifier modules.

Globes fitted to the old mains power rocker switch for good looks.

 

At the end of all of these upgrades it was well worth the effort as the hiss, hum and noise has completely gone.

The original looks of the Series 5000 was maintained from all sides except for the rear panel.

However the power supply was split into two separate supplies like two mono blocks in the same case.

 

The main thing is that the amplifier sounds excellent and has not missed a Hz since.

 

PS: The silvered mica capacitors seen in some pictures were replaced with polystyrene types as these sounded the best IMO.

 

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Getting geared up to restore my old ETI Series 5000 power amp (which uses the ETI 477 David Tilbrook designed mosfet boards ) I was not happy with the original boards, as some of the tracks li

In January - March 1981 ETI published construction articles for the Series 5000 Mosfet stereo power amplifier, Project 477, designed by David Tilbrook. Jaycar Electronics had made a complete vers

Some more pics

My brother did and did not use non inductive resistors and all hell broke loose. Mad oscillation.

That's what I think could have happened on the day my Series 5000 had it's turn perhaps.

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34 minutes ago, MarcAL said:

My brother did and did not use non inductive resistors and all hell broke loose. Mad oscillation.

That's what I think could have happened on the day my Series 5000 had it's turn perhaps.

I built both the ETI5000 AEM6010 the 100W @ 8ohms  and then the AEM6000.  All three never had mad oscillation, the 5000 and 6010 I used typical wirewound that was plentiful everywhere, even if you look into a ME they were using the same.   The 6000 I found Stuart Electronics in oakeigh (no longer there) supplying metal plate resistors.    

Using Polystyrene can be a PITA,  the values change permanently with heat..  One thing I realised is that even the boys at Silicon Chip has discovered, replacing all ceramic caps actually gave a design better THD figures.    

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They are silvered mica capacitors that would not fit on the top side of the amplifier modules at the time.

I used polystyrene capacitors to replace the ceramic capacitors in the signal path only.

I replaced all of the silvered mica capacitors with polystyrene types in the end and that is what I have today but I know I have not supplied a recent picture of them.

Sorry for any confusion as what was done in what order over time, as it can get lost or out of sequence. This is probably why it is necessary to put all of this down on paper or documented.

Some of the previous pictures show the polystyrene capacitor locations on the earlier upgrade. They sounded better to me so I re-installed them only recently.

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Thanks for the info.

Would be very interested to know exactly what caps you ended up choosing.

 

The yellow ( and orange ) ones on the back of the boards ?

 

You mentioned Snubber capacitors across each rectifier diode?  Is this where each diode in the bridge has a cap put across it ( parallel ), so 4 caps per bridge ?

What type / value did you settle on ?

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The snubber capacitors type that I would use now would be MKP10 0.01uF 1000VDC by WIMA as I keep these in stock now for these types of applications.

The ones shown in the pictures and used here are MKP 0.1uF X2 275V mains capacitors and were also used across the mains IEC socket.

I used them because I only had these at the time however do use this value for the IEC mains socket if you choose to do so.

However either will work as a snubber but the WIMA MKP10 were designed more for this application so use that value for the bridge rectifiers.

 

The yellow caps that were used on the underside of the amp modules are Metalised Polypropylene 250V PMT types as I preferred these over the green caps supplied in the kit.
The orange caps are ceramic 400V types which are only to help with oscillation problems associated with the power mosfets, the existing ones that came with your kit should still be okay.

 

As I was building new modules from scratch I dispensed with the idea of recycling components that were cheaper to buy and rely on than to trust second hand salvaged parts.

So some component choices were made only for the sake of trying something hopefully better as you can always go back to the original types if you don't succeed.

That was the case that I found with the silvered mica capacitors which I used to replaced some of the green caps, so I went back and changed them to polystyrene in the end because they sounded better to me which was confirmed only by trial and error

.

You will never know if you don't explore however if someone from reputable experience knows then why not try that as well.

The worst thing that can happen is to blow up the Hitachi mosfets or some Altec's....

 

Sorry for that last comment as it was totally out of bad taste.

Take care, research and choose wisely.

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6 hours ago, Addicted to music said:

I built both the ETI5000 AEM6010 the 100W @ 8ohms  and then the AEM6000.  All three never had mad oscillation, the 5000 and 6010 I used typical wirewound that was plentiful everywhere, even if you look into a ME they were using the same.   The 6000 I found Stuart Electronics in oakeigh (no longer there) supplying metal plate resistors.    

Using Polystyrene can be a PITA,  the values change permanently with heat..  One thing I realised is that even the boys at Silicon Chip has discovered, replacing all ceramic caps actually gave a design better THD figures.    

So out of curiosity how did your AEM6010 and AEM6000 perform under inductive and capacitive loads?

The ETI Series 5000 was remarkable as it never faulted under load tests once the non inductive, 5W, 0.22 ohm resistors were installed.

Even when a 4KW, 3.5 ohm inductive load wire wound resistor from an elevator dynamic braking unit was being used for load tests.

However not all Mosfet power amplifiers are able to withstand that test.

I have carried out this test on many power amplifiers over the years and was very surprised to find even very reputable ones failed.

My hat goes off to ETI for this one.

 

On another note the power rating from these tests on my amplifier were less for each channel driven due to the fact that the power supply transformers were separated.

The original design had these combined in parallel and used only one bridge rectifier which you may want to consider if you require 100W into an 8 ohm load.

 

As with Polystyrene capacitors as long as you don't over heat them when soldering them in and choose not to place them in hot spots they will be okay and not alter their value.

An alternate way to be sure of the value of some components is to measure them in situ where possible providing you have access to such testing equipment.

It can be done but that too can be a PITA.

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2 hours ago, MarcAL said:

So out of curiosity how did your AEM6010 and AEM6000 perform under inductive and capacitive loads?

The ETI Series 5000 was remarkable as it never faulted under load tests once the non inductive, 5W, 0.22 ohm resistors were installed.

Even when a 4KW, 3.5 ohm inductive load wire wound resistor from an elevator dynamic braking unit was being used for load tests.

 

A mate of mine had all the test gear.  He used a jug element for the output and yes he used water to ensure it’ll survive.  Those Hitachi Mosfets were indestructible if you never exceed Vgs.  We even short circuited the output just for fun!  

Then he left for Grease!    So I’d never got to test my 6000 out like he did.  But in saying that I’ve used mine to drive 1.8 ohm ribbons with a 180uf MKP cap,  parallel with a 1.6mH inductor that’s hooked up to 2 Eton 11” in parallel since 1994.  The 6000 has been driving these in this arrangement since it was up and running.  No issues for almost 25yrs.    

The 6010 was testing the water waiting for parts for the 6000.  Certain parts like Wilma caps only came as samples or quantities of 1000s.  So some stuff you just had to wait.  That’s why it took so long for my 6000 to get up and running.  

I’ve  moved on now and back to BJTs.    I’d probably never build a mosfet amp again.  However some of those Pass Labs are interesting.

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8 hours ago, Addicted to music said:

A mate of mine had all the test gear.  He used a jug element for the output and yes he used water to ensure it’ll survive.  Those Hitachi Mosfets were indestructible if you never exceed Vgs.  We even short circuited the output just for fun!  

Then he left for Grease!    So I’d never got to test my 6000 out like he did.  But in saying that I’ve used mine to drive 1.8 ohm ribbons with a 180uf MKP cap,  parallel with a 1.6mH inductor that’s hooked up to 2 Eton 11” in parallel since 1994.  The 6000 has been driving these in this arrangement since it was up and running.  No issues for almost 25yrs.    

The 6010 was testing the water waiting for parts for the 6000.  Certain parts like Wilma caps only came as samples or quantities of 1000s.  So some stuff you just had to wait.  That’s why it took so long for my 6000 to get up and running.  

I’ve  moved on now and back to BJTs.    I’d probably never build a mosfet amp again.  However some of those Pass Labs are interesting.

Yes the Hitachi mosfets are almost indestructible. I have some on a commercial amp that have failed and it is probably due to exceeding or being very close to Vgs limits.

I will get back to fixing that one when I can get my hands on some 2SK135, 2SJ50, 2SK176 or 2SJ56 types if availability comes my way.

I would not care if they were second hand either as beggars can't be choosers when it comes to these discontinued Hitachi devices.

Although I do remember that some one did say that they would be remade some day soon, but I am still waiting...

Yes, Pass Labs are very interesting, very well designed and made.

 

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  • 4 weeks later...

Checked out the  diyAudio  web site and found a simple modification using an 18v ( 2 9v in series) zener across q7 and q8

It is said that it reduces dissipation and is endorsed by David Tilbrook himself !

Very hard from the picture to tell exactly where it is connected. The thread is a bit old and I have asked the question, but have had no reply as yet.

 

There was talk of another mod that involved where the NFB was taken from. Apparently this can help reduce distortion as well.

 

Does anyone  know about these mods ??

 

eti 477 pcb.jpg

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20 hours ago, Leinster Lad said:

Checked out the  diyAudio  web site and found a simple modification using an 18v ( 2 9v in series) zener across q7 and q8

It is said that it reduces dissipation and is endorsed by David Tilbrook himself !

Very hard from the picture to tell exactly where it is connected. The thread is a bit old and I have asked the question, but have had no reply as yet.

 

There was talk of another mod that involved where the NFB was taken from. Apparently this can help reduce distortion as well.

 

Does anyone  know about these mods ??

 

eti 477 pcb.jpg

I haven't read the article on the modifications you mentioned but see the picture of where the Zener diodes are located (green box outline).  The diodes are wired in series so that blob of solder between the two is only connecting the two diodes together. It should not be touching any other part of the circuit.

 

If the original mod calls for an 18v Zener I'm surprised that they used 2 x 9v???? in series.  Rationale is 9v is not a common Zener voltage whereas 9.1v is.  Therefore 2 x 9.1 = 18.2v not 18v.  On the other hand, 18v IS a common Zener voltage. 

 

Those Zener diodes in the picture look like typical 500mW or 1W glass encapsulated varieties in a DO-41 packages wired in series.  Probably 1N757 types or similar. You'd have to refer to the original mod text to find out for sure.  However a single 18v Zener like a 1W 1N4746 should probably be adequate if indeed the correct Zener voltage is supposed to be 18v.  In fact any Zener diode of about that voltage would reduce dissipation in that part of the circuit by reducing the C-E voltage drop across both Q5 and Q7, but 18v is probably what is across RV1 when the quiescent current is correctly adjusted.

 

For the purpose of the discussion I am assuming you are referring to this thread?  

https://www.diyaudio.com/forums/solid-state/134481-eti-477-resurrected-2.html

 

 

Cheers,

Alan R.

5000 series MOSFET mod.jpg

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Correct Alan, that is the diyAudio thread that has mentioned the mod.

 

There is very very little detail surrounding the mod. Specifically exactly how and where the zener is connected.

Why 2 x 9v instead of the more common 18v ?

Looks like the zeners are connected between the collectors of Q5 and Q7 ( track needs to be cut )

 

If the VAS stage is so unbalanced, why not design it properly instead of a patch job ?

 

Another diyAudio contributor to that thread mentioned fitting a 200ohm trim pot to balance the circuit, but gives no detail of where to fit it or how to measure the "balance"

 

 

 

 

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31 minutes ago, Leinster Lad said:

Correct Alan, that is the diyAudio thread that has mentioned the mod.

 

There is very very little detail surrounding the mod. Specifically exactly how and where the zener is connected.

Glad that I was referring to the correct thread.  A tad embarrassing if it wasn't. 😜

 

It isn't all that common that people forget that they knew what they were doing or intended to do, but this usually gets lost in translation. 

Other times people just want to tell you all about how wonderful the mod is / was but conveniently don't share the detail. 🤐

 

31 minutes ago, Leinster Lad said:

Why 2 x 9v instead of the more common 18v ?

Maybe that's all they had available at the time?  Could be that they used 1W Zeners so up to 1W of power dissipation across each?  2W Zeners aren't common standard types, but based on the circuit it's unlikely the Zener(s) would be dissipating much power.

31 minutes ago, Leinster Lad said:

Looks like the zeners are connected between the collectors of Q5 and Q7 ( track needs to be cut )

Yes, that's the only way the mod would work.

31 minutes ago, Leinster Lad said:

If the VAS stage is so unbalanced, why not design it properly instead of a patch job ?

I didn't design it and only the designer would know why they made it that way.  Minimise component count?  Simplified board layout?  One less part to fail?  Only David Tillbrook knows (I assume he was the designer).

31 minutes ago, Leinster Lad said:

Another diyAudio contributor to that thread mentioned fitting a 200ohm trim pot to balance the circuit, but gives no detail of where to fit it or how to measure the "balance"

That would work but why bother with a trimpot instead of the Zener ?  If the aim is to reduce dissipation in Q5 and Q7 a simple fixed resistor would do the same.


The only thing Q5 and Q6 share is a common resistor (R17) connected to their emitters.  Q7 has the base and collector connected together so it's really just operating as a glorified diode.

Cheers,

Alan R.

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1 hour ago, Leinster Lad said:

Ok, i have discovered the rason for that cap (blue) that is fitted on the copper side between the sources of Q9 and Q11 🤗

 

 

 

 

Oscillation mod #1.JPG

This is the advantage of having access to and carefully reading the original article and any errata published.

The resistors in question must be non-inductive types.  Most high powered wirewound resistors exhibit some inductance, but the amount of inductance depends on how they are wound.  There are techniques such as Ayrton Perry winding that virtually cancels out any inductance.

 

Parts ain't always just "parts" 😛

 

 

Cheers,

Alan R.

 

 


 

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Take this with a grain of salt.

 

I didnt build the 477 but a lot of the design followed into the 5000.  The AEM6000 was suppose to be a revamped build.  

 

 I’d like to be corrected if I’m wrong.  But one needs to look at the type of transistors and it’s voltage ratings.  For a mod to have a zener to limit to 18.1V to be “approved “ by the designer should ring alarm bells.  And someone I knew at the time was telling me that those transistors should not have  been selected for the job, and that’s b4 I heard there was a mod!   Id like stand corrected if I’m wrong!

 

The green caps mounted on the copper side of the pcb is to reduced self oscillation for Q9 and Q10 to reduce parasitic inductance introduced by components and there leads.  The other reason is to mount them on the bottom side is to get the components as close to those points on the connection as possible.  In those days SMD was unheard of in DIY and electronic companies in Japan were introducing them in the mid 80s.  Today, you wouldn’t  be seen without the use of them to counter self oscillation.

 

ive moved on from the AEM6000.  It  wiped the floor of all the Naim gear I had in the 80s.  But for many years I’ve always thought something was missing.  It wasn’t I returned to Audio and went to a show where Dan DAganstino’s creation showed me what’s possible.    I’m no longer pursuing Mosfets designs,  much prefer the BJTs.  Even all the latest Silicon Chips are using BJT.  One needs to move on from a design that is now over 30yrs and was taking advantage of the introduction of Mosfets.  30yrs on,  and Hitachi, Toshiba Mosfet range have been ditched!  And that includes vfets!     You see many manufacturers come and go, but the standard BJT has always been there!   That on its own should tell you something.

 

 

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On ‎21‎/‎10‎/‎2018 at 6:35 PM, MarcAL said:

 

Jaycar Electronics had made a complete version of the kit available for only $299 and a "BLACK MONOLITH" version of the kit for $319.

The main difference between the two kits was that the "BLACK MONOLITH" version had Beryllium Oxide washers, heatsink grease and the special driver transistor heatsinks.

 

Unfortunately the Beryllium Oxide TO-3 washers for the power mosfets had to be replaced as some of them had cracked into pieces so these were replaced with silicon types.

Beryllium Oxide - no thank you.  One of the most toxic substances around.  It was at one stage there the flavour of the decade when it came to thermal washers and it was even mixed into thermal paste.  Some techs would apparently apply it with their bare fingers.  :(  Thank goodness it's almost unobtainium to the amateur constructor because nobody bothers to read the MSDS.  There is even a name for the disease if it was breathed in - berylliosis.

 

Cheers,

Alan R.

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17 minutes ago, Monkeyboi said:

Beryllium Oxide - no thank you.  One of the most toxic substances around.  It was at one stage there the flavour of the decade when it came to thermal washers and it was even mixed into thermal paste.  Some techs would apparently apply it with their bare fingers.  :(  Thank goodness it's almost unobtainium to the amateur constructor because nobody bothers to read the MSDS.  There is even a name for the disease if it was breathed in - berylliosis.

 

Cheers,

Alan R.

I wouldnt be a bit surprise if I had used my bare hands handling beryllium oxide mixed in thermal paste...  when I started work,  I realised I became a glorified  cleaner.  One of the things they use to get me to do which was common practise in the industry was to polished Selenium drums doped with arsenic with brasso.  That was done with brasso applied to a piece of rag and then polished the drum till you get a smooth surface.  Some of the roller cleaners from the 80s are no banned!  Too dangerous with the high potential to cause cancer.  So now we enter an age where I can’t even carry compressed air!   So no isopropyl alcohol, no actetone no WD40 or pressurised Triflo.  

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I have read all the preceding comments with great interest, as I recently scratched out my "beginnings" of the ETI 5000 Amplifier kit build. ay back in the 1980's I bought a Hitachi MOSFET Amp (HA-7700) that utilises the slightly lower spec MOSFETs from Hitachi (2SJ48's and 2SK133's). I still have it today and it has amazing sound.

 

Because I owned this amplifier, I was most intrigued by the article in the ETI publication way back. I started with great intensions to build this amp, purely for the experience but never got down to actually building it.

 

Over the years I have relocated residence a few times and my boxes of goodies just followed me around. I recently retired form employment and started sorting out my stuff and I was so excited to find my set of (Hitachi J50's and K135's), my two circuit boards and the mains transformer I bought for the project.

 

To my great frustration I cannot find my documentation to build the amplifier.

 

I would really appreciate your assistance if one of you could share, with me, the schematic diagram, component list and the circuit board layout.

 

It will a whole lot more exciting to tackle now that I have read all of the development improvements in the above chat.

 

In great anticipation.... thanks for sharing all of your experience and skill above.

 

 

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12 hours ago, AntonEB said:

I would really appreciate your assistance if one of you could share, with me, the schematic diagram, component list and the circuit board layout.

 

It will a whole lot more exciting to tackle now that I have read all of the development improvements in the above chat.

 

In great anticipation.... thanks for sharing all of your experience and skill above.

 

 

Hi Anton,

 

If somebody here doesn't have the original magazine article it can be purchased for download from here - http://www.siliconchip.com.au/Shop/17   It's under AUD10 which is about 100 Rand.

 

Scroll down the page to the relevant article.  Silicon Chip magazine now own all the IP of ETI.

 

Cheers,

Alan R.

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15 hours ago, AntonEB said:

I have read all the preceding comments with great interest, as I recently scratched out my "beginnings" of the ETI 5000 Amplifier kit build. ay back in the 1980's I bought a Hitachi MOSFET Amp (HA-7700) that utilises the slightly lower spec MOSFETs from Hitachi (2SJ48's and 2SK133's). I still have it today and it has amazing sound.

 

Because I owned this amplifier, I was most intrigued by the article in the ETI publication way back. I started with great intensions to build this amp, purely for the experience but never got down to actually building it.

 

Over the years I have relocated residence a few times and my boxes of goodies just followed me around. I recently retired form employment and started sorting out my stuff and I was so excited to find my set of (Hitachi J50's and K135's), my two circuit boards and the mains transformer I bought for the project.

 

To my great frustration I cannot find my documentation to build the amplifier.

 

I would really appreciate your assistance if one of you could share, with me, the schematic diagram, component list and the circuit board layout.

 

It will a whole lot more exciting to tackle now that I have read all of the development improvements in the above chat.

 

In great anticipation.... thanks for sharing all of your experience and skill above.

 

 

 

What you seek can be found .......  Here    ( please note that I am not the owner of these documents )

 

The ETI477 / Series 5000 amp was published in ETI 1981 Jan, Feb, March

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Got an answer from the diyAudio forum regarding the zener and NFB mods.

The zener is self explanatory.

You can clearly see that the track between the collectors of Q5 & Q7 is cut.

 

The NFB ( R19 22K) now gets connected to the exact same point as L1 (inductor)

In the picture, you can just see the tail of R19 running parallel to the track and terminating at L1

 

I am guessing that this gives a more accurate reference point of the output signal ( without any variations caused by current flow )

Like the theory behind a star point ground system.

 

eti477 resized.JPG

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  • 1 year later...

Getting geared up to restore my old ETI Series 5000 power amp (which uses the ETI 477 David Tilbrook designed mosfet boards )

I was not happy with the original boards, as some of the tracks lifted when I depopulated them.

 

So, after a LOT of pain etc, I managed to copy the board design, created the Gerber file and had some (10) new boards made !

 

So if anyone needs a new board or two, hit me up !

IMG_1820.JPG

IMG_1821.JPG

IMG_1822.JPG

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Hi Leinster Lad,

 

It's good to hear from you again and getting back onto this project.

 

I noticed that the boards are not drilled so I figured that one could use one of the old boards as a template and drill through that to keep it as accurate as the original.

 

The soldering of the tracks would be a thing to sort out and would be open to suggestions.

 

I'll PM you about these magnificent boards shortly.

 

Keep up the good work!!

 

MarcAL.

Edited by MarcAL
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Hi MarcAl, nice to hear from you as well !

 

You are correct about the boards being undrilled.

I will use one of my old (naked) boards as a drill template, so I wasn't worried about creating a "drill file" for the PCB manufacturer (I also had no idea how to create one, so the decision was easyB))

 

I also have a couple of mods that I want to do which might require different size holes, so I have left my options open. (i.e. screw connectors for power inputs and output etc.) 

The 18v zener

10 turn pot for the mosfets bias, or even a daughter board for the bias  as per the EAM6000 amp.

Maybe clipping indicators as per the EAN6000 as well.

Actually lots of ideas from your previous rebuild as well as the good folk over at diyAudio.

 

I may also split the power supply between the drive side (regulated) and the output side (unregulated) at the fuses ? (like Naim do ?)

Not really sure yet. I have got myself a scope and you-tube , so I will be experimenting a bit !

 

Hope I don't let too  much smoke out !!

 

Regards

Dave

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On 24/11/2018 at 2:01 PM, Leinster Lad said:

 

What you seek can be found .......  Here    ( please note that I am not the owner of these documents )

 

The ETI477 / Series 5000 amp was published in ETI 1981 Jan, Feb, March

Archives are now gone.

I think SC sent him a lawyers letter for copyright breach ?

 

Anyway, I have scanned a heap of my SC and ETI mags if anyone needs a specific article.

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  • 1 month later...
On 12/08/2020 at 5:34 PM, Ozcall said:

Have been tempted over the years to buy a pair of these. Haven't got  round to it yet but they do look the part to my layman's eyes :

https://connexelectronic.com/product/aem6000-audio-amplifier-with-heatsink/

AEM6000.jpg

 

They are a rip off of diy audio member suzyj rework of the original design.

 

https://www.diyaudio.com/forums/solid-state/288479-aem-6000-ready-build-post5555673.html

Edited by WINEDS
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Yep, they certainly did rip Suzy off.

From what I have read, she designed and developed an absolutely cracking amp.

Unfortunately, she is not (able?) to support her work and sell boards etc.

 

These connex guys have just filled a vacuum created by that. Sad really. I'd by a pair of her boards in a heart beat.

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