Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kasperbergholt on February 02, 2025, 08:21:57 am
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Hello all,
Some time ago, I got some really great input on a questions about the different characteristics of both input (6CS7) and output tubes (EL34, 6L6GC, 6NC3-E (https://el34world.com/Forum/index.php?topic=31610.0)).
Now, I have a very simple preamp on the way, based on 2 x ECC81 family tubes and 1 x 5U4G family of rectifier tube.
In my stash, I have the following tubes from the ECC81 family:
Telefunken ECC81, circa 1980
General Electric 12ATWA, circa 1960
Electro Harmonix 12AT7 (new production)
I’ve never had any equipment with rectifier tubes from the 5U4G family before, so I’d like to learn more about whether certain combinations create good synergy.
American versions paired with American tubes? Or European versions with European tubes?
I think VT-244 tubes look absolutely stunning, aesthetically speaking, but they’re also quite pricey.
The first one I’m going to try is a Svetlana 5UC3 from 1974.
Looking forward to hearing your thoughts, experiences, suggestions, and good ideas—also where the best bang-for-the-buck options are, and/or what’s overpriced or known for defects/short lifespans.
(https://bergholt.net/wp-content/uploads/2025/02/5U3C-svetlana-1974-tube-nos-scaled-e1738427697287.jpg)
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I believe that the rectifier and the PI tube are completely separate issues. The rectifier influences the B+ voltage in the whole amp, which could affect anything in the amp. Then, it influences sag, that is, the dynamic behavior of the amp in or near limitation. The differences between tubes from different manufacturers are much smaller than, e.g., the difference between a directly and an indirectly heated rectifier.
The PI tube can have different gain and perhaps different clipping (which is not likely in PI), but this nearly unrelated to the B+ rail.
I am pretty sure no manufacturer put there any synergy intentionally.
Good luck.
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Datasheet say you which are his spec and performance, this are the only thing important
OK, may be you want to build (for aestetic reasons) a full octal or seven pin circuit but this regards only aestetic if you find tube with the spech you are looking for
Franco
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If I understand correctly, the question was about equivalent tubes of different make; of course ECC81 of any make is interchangeable with 12AT7anything, 5U4G is VT-244 is 5C4S, but people say they hear sonic differences. BTW sag is probably the reason to use 5U4G with 15W of filament power and nearly 50V voltage drop at full power.
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Thank you for the feedback, jansch, kagliostro. It's appreciated.
My basic question is on the pairing.
Possibilites for rectifiers: 5U4G, GZ31, VT-244, 5Z4P, 5UC3/5CS3 (American, Russian, European)
Input tubes: 12AT7 family, ECC81, CV455 (American, European, British)
I know they're equivalent enough for use in the circuitry in question.
Would matching e.g. an American rectifier tube with an American input tube make a difference? Or a European with a European?
Or won't there be any cross-interchange between the two in terms of sound?
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Would matching e.g. an American rectifier tube with an American input tube make a difference? Or a European with a European?
Interracial mixing was a bigger deal for amps made before the 1960s, modern amps are mostly relaxed about it.
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^LoL^
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The function of the rectifier is to eliminate AC that comes from the wall (via the PT), so as to leave pulses of DC which the filter cap rail converts into high VDC to provide a high voltage source for the audio amplifier.
As far as your preamp tubes are concerned, each 12AT7 triode will only draw around 1 to 2 mA from the high voltage supply (maybe at most 3 or 4mA depending on how each stage is configured for DC). A 5U4 (any working 5U4) can supply way more than that before it starts to putter out. So it wont make any difference which brand of 5U4 you use or which brand of 12A_7 you use - as long as the tubes aren’t damaged or worn out.
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The function of the rectifier is to eliminate AC that comes from the wall (via the PT), so as to leave pulses of DC which the filter cap rail converts into high VDC to provide a high voltage source for the audio amplifier.
As far as your preamp tubes are concerned, each 12AT7 triode will only draw around 1 to 2 mA from the high voltage supply (maybe at most 3 or 4mA depending on how each stage is configured for DC). A 5U4 (any working 5U4) can supply way more than that before it starts to putter out. So it wont make any difference which brand of 5U4 you use or which brand of 12A_7 you use - as long as the tubes aren’t damaged or worn out.
Thank you for the clear and detailed explanation, tubeswell, especially the breakdown of how the rectifier tube works and how little current the preamp tubes actually draw.