Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on December 11, 2018, 11:39:05 am
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HI all, I just built a push pull 6BG6 version of a Princeton Reverb on an old chassis I have laying around. These tubes are electrically identical to a 6L6g.
For the power transformer I used an old Chicago Transformer potted transformer that originally came from a scrapped out mono hifi cabinet I picked up. That amplifier was running a pair of 6L6s, same as my amp. I didn't know the specs of that transformer when I started to build (couldn't find them online) but as it was running the same output tubes I planned to use, I figured it was fine. The original 6L6s were tired so I assumed the amp had been used for many years without problem. It was also running a 5U4.
This morning I found the specs and I have some concerns. According to the catalog I'm using the transformer (Stancor Chicgao PCC-105) has:
345-0-345 hv secondary at 105ma.
6.3v at 3.5a
5v at 2a.
SO I've got two problems. I'm going to have to ditch the 5U4 I was using as I don't want to stress that 5v winding.
Also the current rating of the hv secondary seems awfully low for what I'm doing.
Should I down the bias a little more, maybe around 50, to keep that secondary from saturating too much? It's currently at about 60 percetn and putting out 23w or so.
It just seems weird to me that given these specs, this transformer was used in a hifi amp with a 5U4, probably for many years, without problems.
What would you all do?
Thanks!
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Free is the key here :icon_biggrin:
If "they" used 6L6 and 5U, run it til fail, I bet it lasts long enough to get bored with it, then.........
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It probably ran with 8K load. What are you loading it with? If the usual Bassman 4K OT, expect double current.
Are the make/model of hi-fi, and the model of the PT, secrets?
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I have used a 5R4GYB with good results. It has 2 amp heater and dropped B+ 13 volts lower than a 5U4GB. Is your speaker impedance the same as the original amp? Trying to understand whether the load seen by the output transformer has changed with your new circuit.