Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on February 20, 2011, 02:04:43 am
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I'm building an SE bass amp which is based on BF Champ (AA764)
and would like to ask which one of the following transformers I should
use as a PT. I'll use an SS rectifier with big filter caps. The power amp should
also be compatible with EL34, 6550 and 5881.
1. 350V-0-350V/180mA
2. 275V-0-275V/250mA
/Leevi
(http://)
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HI Leevi, The stock PT i got for my Champ was 325-0-325v that gave me with SS rect 430v which is more than enough for the 6L6/EL34.So i guess your stuck in the middle.The 275-0-275v will be in the safe range giving about 385v after rect,and the 250mA will be more than enough.I think the 350-0-350v might be a bit high and the 180mA a bit tight but you might need a second opinion :smiley:Hope this helps.
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You can always go high and use Zeners to bring the voltage down, if needed.
al
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Both would be fine I guess.
I would use the 350VAC one myself, for a 450 / 500V B+.
It's a bass amp, right? Then the tighter the sound, the better, and high B+ will deliver just that.
180mA sounds ample to me.
Just MHO.
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Yes, it's a bass amp. For the 6L6 the B+ is over the limit but I think even Fender uses
more than 400V voltages with the 6L6s.
/Leevi
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IMO the best bang for the buck is the Allen TP25. It will handle the 6L6 perfectly, the voltage won't be too high and it's designed to be used for a champ or Princeton amp upgraded to 6L6 power tubes. You can use a 5Y3 or a 5AR4, but for bass I would use SS rectification and a little more filtering. I would think with the SS rec you could use a KT88 but I would contact David first. He also sells a really nice inexpensive Champ chassis and many Parts for this type of Amp. I tried many OTs for a champ and his models sounded the best. But you can go with one of those huge Hammonds which sounded good too but were expensive. Doberman also has a very good 20watt or so SE OT with many taps for about $60 last time I looked.
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IMO the best bang for the buck is the Allen TP25That's certainly a good PT for that purpose. One problem concerning this transformer is the primary because
it should be 230V. As an OT I'm going to use Hammond 1627SEA which is quite expensive but I hope it gives
value for my money.
http://www.hammondmfg.com/1627.htm
/Leevi
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for $25 this is all you really need - best value really for new.
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jojokeo,
Yes, but the primary should be 230V. The secondary 100mA is probably not enough for 6550.
/Leevi
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Is money an issue? Hammond makes some great stuff but there are other companies too. Hammond trannys are also overbuilt, I can't say that about any others that I haven't worked with. The Allen, MM and Heyboers, the ones Doug carries all good.......Hammond too. So I would either use a Hammond or one made in your area/country that's a little over spec.
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Sorry Levi I missed the input voltage comment.
How ya doing BD?
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Sorry Levi I missed the input voltage comment.
No problem. I have previously used Weber's transformers and have been satisfied with them.
Unfortunately the so called "Universal" transformers are more expensive and when you add overseas shipping,
taxes and customs to the price it is not any more so economic.
/Leevi