Best Application For My Vintage Power Transformer

[Digital Man]

Does anyone here have a schematic for a 45 SET Stereo audio amp ? I have tried google with no luck, I have a guy who can build me the amp, but he needs me to provide him with said schematic first. Thanks.

Edited April 1, 2019 by Digital Man

[Ian McP]

https://www.google.com/search?client=firefox-b-d&ei=CMqaXI_sFoXGrQHeoKr4Dg&q=45+Single+ended+Triode+schematic&oq=45+Single+ended+Triode+schematic&gs_l=psy-ab.3..33i160.10428.14520..14857...0.0..0.229.1698.0j9j1......0....1..gws-wiz.......0i71j33i22i29i30j33i10.1lbIaMdgCSg

 

output transformers etc

http://www.hammondmfg.com/5cindex.htm

[Digital Man]

Hi, I googled those links earlier, I need something else, they are mostly 23A plus 45 schematics, I am after a purely 45 schematic, thanks anyway

[RoHo]

That's because you can use virtually the same circuit with a 45 or 2A3 valve with just a few changes to the power supply voltage, heaters and output valve biasing.

[Digital Man]

Hi, I realise that, that is why I and after purely a dedicated 45 schematic. Thanks

[Ihearmusic]

What tube will you use to drive the 45?

[Digital Man]

Hi, I'm not to sure yet

[RCAJack]

Have you bought any parts yet? You could do a direct-coupled amp like a Loftin White, or a transformer coupled design, or any number of cap coupled designs. There would be budget and sound implications in choosing any circuit. Sounds like a great project once you line up your requirements. 

 

I think this this is a good write up on a design that can accommodate the 45 or 2A3 but the primary impedance of the OPT is (AFAIAW) what makes it suit one valve better than the other. 

 

http://jelabsarch.blogspot.com/2012/06/je-labs-simple-452a3.html?m=1

[acg]

Here you go.

 

Of course I've not heard it or any of its variants, but it should be very good. 

 

Which circuit you actually have built depends on how you are going to use the amplifier.  In my case I have a 2.5V/4V DHT circuit for my midrange channel only so can get away with a direct coupled circuit because it does not have to handle bass.  The result is stellar.  Being single ended, the output transformer should match both the speaker load that it is driving and the load required for the 45 tube which happens to be the same for both the 2A3 and 45's...so worry most about getting the best output transformer for your particular job which is where you should sink most of your $$$.  The OPT is the biggest determinant of sound in the entire circuit so get it right.

 

The multi-tube 45/2A3 circuits are just as perfectly capable as a specialised circuit for either valve so certainly do not look past them.

[Digital Man]

Hi Guys, Sounds good, I did scavenge a power transformer from a radiogram, it was running 6V6GT's in SE mode, the power transformer, which could be a AWA transformer, only guessing, no markings on the transformer to identify, Heater voltage is 6.3 VAC, HT for rectifier tube is 400 volt, has a 5 volt AC tap as well for the rectifier heater, physical capacity is 60VA, it Ould be more

Edited April 1, 2019 by Digital Man

[Digital Man]

If this power transformer does not suit a 45 tube, then I am open to suggestions, I intend to use this power transformer in one way or another, set being my first preference

[acg]

5 minutes ago, Digital Man said:

Hi Guys, Sounds good, I did scavenge a power transformer from a radiogram, it was running 6V6GT's in SE mode, the power transformer, which could be a AWA transformer, only guessing, no markings on the transformer to identify, Heater voltage is 6.3 VAC, HT for rectifier tube is 400 volt, has a 5 volt AC tap as well for the rectifier heater, physical capacity is 60VA, it Ould be more

400V for B+ should be fine, assuming it is capable of providing enough current.  Being a DHT, under all circumstances I would run a separate transformer for the heater especially if you use AC heating (which I do).

[Gryffles]

Agree with @acg that the Bartola circuit should be very good indeed.

My preamp is one of his designs and is excellent.

 

 

[Digital Man]

Hi Guys, Okay, thanks for the link, I am thinking of changing the title for this thread, since my tech friend has informed me that all of the voltages from my transformer are too high and will instantly blow the 45 tubes once switched on, unless someone has other thoughts on how to make this transformer work with 45 SET. Thanks.

[Gryffles]

13 minutes ago, Digital Man said:

Hi Guys, Okay, thanks for the link, I am thinking of changing the title for this thread, since my tech friend has informed me that all of the voltages from my transformer are too high and will instantly blow the 45 tubes once switched on, unless someone has other thoughts on how to make this transformer work with 45 SET. Thanks.

Why not just get a different transformer? Power transformers are relatively cheap it's the OPT's that can cost a lot depending on your goal.

[Digital Man]

Hi, No, not at this stage, I want to use what I have, if that means that the power transformer that I have is too big to run a 45 tube, then I will use what I should be using for this power transformer, which, it originally ran 6V6GT's in SE mode

[acg]

1 hour ago, Digital Man said:

Hi Guys, Okay, thanks for the link, I am thinking of changing the title for this thread, since my tech friend has informed me that all of the voltages from my transformer are too high and will instantly blow the 45 tubes once switched on, unless someone has other thoughts on how to make this transformer work with 45 SET. Thanks.

 

What you do is start with a high voltage and then filter it with inductors, capacitors and resistors ending up at the required voltage for the tube.  For example, for my 45/2A3/YO186/RE604 amplifier the B+ from the transformer is 455VAC which is rectified with Cree Schottky's then an LCLCR  filter which leaves 405VDC at the anode of the power tube.  Your tech friend should know this...the final resistor sets the voltage B+ voltage.

 

If for the driver tube you need to reduce that voltage then just use a RCR filter to drop to (in my case) 140V for the 6E6P.

[acg]

34 minutes ago, Digital Man said:

Hi, No, not at this stage, I want to use what I have, if that means that the power transformer that I have is too big to run a 45 tube, then I will use what I should be using for this power transformer, which, it originally ran 6V6GT's in SE mode

 

1 hour ago, Digital Man said:

Hi Guys, Okay, thanks for the link, I am thinking of changing the title for this thread, since my tech friend has informed me that all of the voltages from my transformer are too high and will instantly blow the 45 tubes once switched on, unless someone has other thoughts on how to make this transformer work with 45 SET. Thanks.

Looking at this again, 400V is could be too low for B+ and you will probably need about 55-60mA current from that winding...I don't know if you've got it or not.  Knocking the 6.3VAC down to 4VAC/DC is trivial but you will have hum unless you (a) use AC heating from a separate transformer or (b) go for DC heating with something like a Coleman Regulator.

[Digital Man]

Hi ace, I have passed on your suggestions. Thanks.

[acg]

7 hours ago, acg said:

 

Looking at this again, 400V is could be too low for B+ and you will probably need about 55-60mA current from that winding...I don't know if you've got it or not.  Knocking the 6.3VAC down to 4VAC/DC is trivial but you will have hum unless you (a) use AC heating from a separate transformer or (b) go for DC heating with something like a Coleman Regulator.

Oops...just noticed that the filament of the 45 is 2.5V, not 4V as I mentioned above.  Either way, it is doable. 

 

The circuit will determine what anode voltage you require and you should be able to drop 400V to whatever you require using a resistor, just so long as your transformer is able to supply the necessary current.

Edited March 28, 2019 by acg

[Ihearmusic]

Are you going to use a tube rectifier?

That will help with dropping the B+ voltage.

I personally would use a DC filament supply. A low power amp requires efficient speakers and you do not want any hum.

Heater current will be high. Is your PT up to it?

Was the radiogram a mono set up?

If so, your PT might be on the low side to supply the mA required to drive a stereo set up.

 

Edited March 28, 2019 by Ihearmusic

[Digital Man]

Hi, I’m not sure if it was mono or stereo, yes, I will be using a tube rectifier

[Ihearmusic]

Depending on the rectifier tube you are going to use you can drop between 10 and 60VDc.  (Current depending)

If one knows the circuit specifics and what driver tube you are going to use, one can estimate the current requirement and then test the PT for its suitability.

But, since a  6V6 tube operates at lower current and requires a 3rd of the filament current of a 45 tube you might find the PT will not be up to the task.

[pulinap]

Also try Patrick Turner's Turner Audio website 

[RoHo]

If you're really keen on the 45 I reckon you can make it work with a 400V transformer.  Use a choke input supply circuit which gives a reduced voltage output compared to a cap input cct.  The textbook says a choke input PS outputs 0.9 x the transformer voltage against 1.4 x for a cap input.  Minus a bit for loss in the transformer.  It's also gentler on the transformer and minimises current "wastage" through a big first cap.  Many SET designers recommend them.  Take off another 50-odd volts for loss through the rectifier and power supply choke(s) and another 50V for the cathode bias resistor.  This leaves you within spitting distance of the recommended 250V(plate to cathode) for an SE 45 output stage. 

Point your tech towards Duncan Amps PSUD power supply  software which is a great, free PS designer.  You get to try lots of different PS designs, voltages and currents without blowing things up.