Tube phono stage ready for Mods

[Stump]

Just sent my Tube phono stage away for some mods.First to increase the gain then to upgrade parts........

[Guest Muon N']

Looking forward to the after pics

 

Lots of Allen Bradley resistors in there, some may have absorbed moisture and now out of spec' , very nice resistors though.

 

This should be interesting as there is a lot of room to move in improving things in this nice bit of kit.

[Stump]

37 minutes ago, Muon N' said:

Looking forward to the after pics

 

Lots of Allen Bradley resistors in there, some may have absorbed moisture and now out of spec' , very nice resistors though.

 

This should be interesting as there is a lot of room to move in improving things in this nice bit of kit.

Thanks ,I put the question on a tube forum and received this reply..

If I was asked to mod this, I’d replace the carbon comp resistors with either Dale 1% or Naked Z-Foil resistors. Replace pow supply caps with high end, larger value, low ESR high ripple current, 10,000hr bits from Panasonic, and bypass them with .1uf film caps. I’d replace any mylar/polyester caps with Polypropylenes. Replace vol pot with a stepped Z-foil unit. That’d be a good start at least. and remove all silver-mica or ceramic caps and replace with polyprop film.

[Mendes]

8 minutes ago, Stump said:

Thanks ,I put the question on a tube forum and received this reply..

If I was asked to mod this, I’d replace the carbon comp resistors with either Dale 1% or Naked Z-Foil resistors. Replace pow supply caps with high end, larger value, low ESR high ripple current, 10,000hr bits from Panasonic, and bypass them with .1uf film caps. I’d replace any mylar/polyester caps with Polypropylenes. Replace vol pot with a stepped Z-foil unit. That’d be a good start at least. and remove all silver-mica or ceramic caps and replace with polyprop film.

Sound advice those naked resistors placed in critical positions make quite a marked improvement from my experience.

[Guest Muon N']

22 hours ago, Stump said:

Thanks ,I put the question on a tube forum and received this reply..

If I was asked to mod this, I’d replace the carbon comp resistors with either Dale 1% or Naked Z-Foil resistors. Replace pow supply caps with high end, larger value, low ESR high ripple current, 10,000hr bits from Panasonic, and bypass them with .1uf film caps. I’d replace any mylar/polyester caps with Polypropylenes. Replace vol pot with a stepped Z-foil unit. That’d be a good start at least. and remove all silver-mica or ceramic caps and replace with polyprop film.

I agree with some of it.

 

The Allen Bradley resistors a very good sounding, they have a very organic natural sound aspect to them, the issue with carbon composition resistors is that they can absorb moisture from the air over time and change spec due to it, some folk who want to use NOS AB resistors will sometimes extract the moisture using an over (the specific I can't recall) to get them in spec again.

 

If absolute transparency and detail are the aim, then metal film and the awesome Z-Foils can achieve that, but you have to be very careful about the balance when choosing parts, as if body (meat on the bones, if I may) and natural sound is very important to you then you can lose some of this in chasing the aspect I mentioned previously.

 

There are some very nice high end offerings in electrolytic caps for power supplies these days, and some of those may not need a film bypass across them, ultimately a film cap replacing the electrolytic's is a good idea, Mundorf offer their 'Tube Cap" in this area, and a couple of other choices are out there depending on available space and budget. But Brands like Jensen and Mundorf have excellent high voltage ranges of quality electrolytic caps and it is questionable if bypasses are needed with these ones.

 

For coupling/interstage caps I prefer the better copper foil types available.....again available space and budget need to be considered as they are usually large and not the cheapest, but fortunately are of small values.

 

It's like the synergy we look for when mixing amps, speaker, sources...............only we are looking at that similar thing on a component level in the circuits.

So, it really depends on what sound you are after when looking at parts, with consideration to the sound of the system as a whole also needs to be considered.

 

Just my thoughts.

 

It's nice that your chassis there is a roomy one and deep in hight

Edited June 22, 2019 by Muon N'
typo

[Guest Muon N']

17 hours ago, Mendes said:

Sound advice those naked resistors placed in critical positions make quite a marked improvement from my experience.

They can definitely have their place

[ophool]

Not to put the dampeners on proceedings, but the little I do know about tube amp design suggests that increasing PSU capacitance in a tube rectified circuit is not to be undertaken lightly nor without complete understanding of the whole circuit and the effects of such change.

Rectifier tubes can be overstressed by too much capacitance following them, chokes and hybrid rectification schemes can affect the desirable values too, but the take away is that increased PSU capacitance is not necessarily "a good thing" and that it needs a very competent valve tech to vary the values to any benefit.

Otherwise, agree with Muon that changing out the AB resistors may lose some of the designed "flavour" - still have fun with it all anyway.

[Guest Muon N']

17 hours ago, ophool said:

Not to put the dampeners on proceedings, but the little I do know about tube amp design suggests that increasing PSU capacitance in a tube rectified circuit is not to be undertaken lightly nor without complete understanding of the whole circuit and the effects of such change.

Rectifier tubes can be overstressed by too much capacitance following them, chokes and hybrid rectification schemes can affect the desirable values too, but the take away is that increased PSU capacitance is not necessarily "a good thing" and that it needs a very competent valve tech to vary the values to any benefit.

Otherwise, agree with Muon that changing out the AB resistors may lose some of the designed "flavour" - still have fun with it all anyway.

Yes the first cap after the rectifier needs to be in a certain range, usually 150uf or lower, with some rectifiers tube 40uf is recommended and either a 37uf or 47uf cap may be acceptable., It's in the data sheet of the given tube.

 

Edit: if that cap after the rectifier is a low value, try Solen BP caps in those power supply positions, or for any lower values if they can be fit.s, in the signal path i would look at better film caps than the Solens.

 

@ophool nice catch there.

Edited June 22, 2019 by Muon N'

[ophool]

As a reference please read the EML datasheet on the 274B rectifier tube and note the capacitance values there.

This does not take into account any other variations there may be in your design which may possibly use a hybrid scheme (partial tube and SS rectification).

For a completely tube rectified circuit pay particular attention to Note 2 at the bottom of the datasheet.

I might be tempted to think that an EML rectifier tube could be a worthwhile upgrade provided the circuit values will not compromise it.  I like the EML tubes in my Yamamoto amp.

Edited June 22, 2019 by ophool

[Guest Muon N']

@ophool Great information for Stump.

 

4uf hay, definitely could use something nice there

 

 

 

 

Edited June 22, 2019 by Muon N'

[Stump]

2 hours ago, Muon N' said:

@ophool Great information for Stump.

 

4uf hay, definitely could use something nice there

 

 

 

 

The only input I will have on the Mods will be payment! The Shop doing the Mods will get access to the Factory schematic and input from the design engineer.They will also have a stock model in house for comparisons.

[Guest Muon N']

17 hours ago, Stump said:

The only input I will have on the Mods will be payment! The Shop doing the Mods will get access to the Factory schematic and input from the design engineer.They will also have a stock model in house for comparisons.

I still look forward to seeing what they do to it

 

But slightly more so, I am hoping that you are very pleased with the result of what every they do to it