Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: blues man on February 22, 2015, 09:59:04 am
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I just had my JJgz34 rec tube blow and replaced it with a fender 5u4m rec tube somebody gave me and the amp sounds so much better. I was getting a little noise occasionally for just a few seconds like bad plate resistor noise ever since I built the amp and every now and then i would blow a fuse. I think now the JJgz34 was a bad tube from the day i got. I noticed more headroom and note definition immediately after i put in the 5u4m. I had the same JJgz34 rec in another amp and it was doing the same thing but I didn't realize it until now. This was not my first bad JJ tube. I don't think I'm going to buy any more of them.
Here is my question. I have a stock 4-10 bassman 5f6a with the main filter caps beefed up to 2 80uf in series (they may be 100uf, Ive got to check and see) and Dougs hot switch mod inslalled. Is the fender 5u4m going to handle the current of a bassman?
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Is the fender 5u4m going to handle the current of a bassman?
Yes. A more important question is "Will the PT handle the extra filament current the 5U4 requires?"
5U4 needs 3 amps. GZ34 only needs 2 amps.
I would prefer to get another GZ34 even if the PT can handle the 5U4. I like the indirectly heated cathode and the extra warm up time of the GZ34.
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The think the PT transformer I have in that amp is a Hammond 290cx and the 6.3vct@4a.
I read an article that said the fender 5u4m rec tubes were made in Russia and they were the only ones made in the 5u4 series that were indirectly heated and were not directly heated like the other 5u4 tubes. I tried a couple of the EH5u4gb in another amp I have and blew 2 of those cause i didn't use the standby switch so I put in a solid state and haven't had a problem with that amp since. I thing Ill try the TAD brand and see what their gz34 is like.
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The think the PT transformer I have in that amp is a Hammond 290cx and the 6.3vct@4a.
The 6.3 VAC secondary supplies heater current to the power and preamp tubes, generally. The heater supply for the rectifier tube is usually supplied by a 5VAC secondary. You should verify that this secondary is up to the task of the increased current demand.
Edited to add: These are the specs I got from Angela.com for the Hammond 290CX PT
Primary 120VAC. Secondaries 325-0-325@180mA for high voltage, 50V bias tap, 5V@3A for rectifier, 6.3VCT@4A for filaments.
Should be okay with the 5U4.