Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: A13X on February 16, 2022, 08:09:41 pm
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Hey everyone, I’ve been doing the current draw calculations on a 5e3 with jj6v6S power tubes and I think this will work, but I wanted to check with the pros.
660v - 100ma
6.3v - 4A
5v - 3A
I understand to be period correct that 660v is too low, but I’ve seen transformer sets for the 5e3 with 660 taps saying that it compensates for higher wall voltages that are present modern day. If this is true, is 100ma enough?
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I have the impression it is a 330-0-330 @ 100mA it might do it.
Look at this: https://www.hammfg.com/electronics/transformers/guitar/deluxe-5e3
https://www.hammfg.com/files/parts/pdf/290BBX.pdf
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I have the impression it is a 330-0-330 @ 100mA it might do it.
Look at this: https://www.hammfg.com/electronics/transformers/guitar/deluxe-5e3
https://www.hammfg.com/files/parts/pdf/290BBX.pdf
Yes, it is a 330-0-330 it says it’s rated for 5-15 watts.
I’m not experienced enough to know how ‘big’ of a difference the extra 15ma is in the PT you linked.
When using a current calculator, it came up at 80ma.
Another forum discussion on a different site, a user suggested that it would be just over 100ma at full signal /w 350v at the plates.
Sounds like the PT I have is slightly too small… ughhh, I was really hoping to save on that expense.
Is there anyone here that would “chance it” for a personal build?
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I'd say go for it.
Depends on what camp you're in.
If you're in the '5E3 can't stay clean loud enough'- camp.. you'd have to build a high power 5E3 with 6L6 tubes, but there are downsides for it doesn't sound like a 5E3 anymore
If you're in the 'Dang! this 5E3 is too loud to crank and get in the sweet spot' .. well, the amp will still be too loud with your transformer.. but you should be good.
Heck, I built a JTM145 2W amp some time ago.. and that still was pretty loud :laugh:
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I'd say go for it.
Depends on what camp you're in.
If you're in the '5E3 can't stay clean loud enough'- camp.. you'd have to build a high power 5E3 with 6L6 tubes, but there are downsides for it doesn't sound like a 5E3 anymore
If you're in the 'Dang! this 5E3 is too loud to crank and get in the sweet spot' .. well, the amp will still be too loud with your transformer.. but you should be good.
Heck, I built a JTM145 2W amp some time ago.. and that still was pretty loud :laugh:
Unfortunately, I usually have to play at low volumes, so for my other amps I get to the sweet spot and then attenuate with an LPad.
I appreciate your response, but I do have a question for clarification.
Wouldn’t an underrated transformer be subject to overheating and damage if the total amp draw of the circuit is higher than rated?
If that’s the case, then I’d imagine it wouldn’t be a question of ‘if’ it can pull the required amps, but rather ‘how long’ it will do it before failure.
I’m guessing it’s a question of what the amp draw is when both tubes are “full on” in the push pull circuit. Is there a rule of thumb of approximately when this happens, or does it only happen a full volume?
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A 5E3 amp will put about the same load on that PT at idle as it will at full roar. If I had that 100mA PT and didn't want to buy a 150mA PT, I'd certainly use it to build a 5E3.
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A 5E3 amp will put about the same load on that PT at idle as it will at full roar. If I had that 100mA PT and didn't want to buy a 150mA PT, I'd certainly use it to build a 5E3.
Thanks so much everyone for the clarification and for saving me $100 on this build!!