Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rhubarb9999 on June 17, 2015, 09:18:55 pm
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So I started with the chassis and iron from an Earth Sounds Super Bass 100 ... essentially a Twin without the reverb. Schematic is almost an exact match. I had the Super Bass running before I gutted it.
I installed a Revolver built Hoffman Twin AB763 board. I removed the first channel bits. So I finally fired it up tonight. Heaters look good, bias looks good.
When I take it out of standby, there is a slight hum in the speaker. I can hear a faint click when I touch the input jacks .. but that's it. I hear no difference when I turn any of the pots. The reverb tank is not installed.
So I noticed a few things. First, the B+ off the 6 diodes is only 318v. Seems low. The diodes took a lot of heat from the soldering tip. Could one or more have been baked?
Second, even though the power transformer has a tap to ground for the heaters, I still ran them to the 100 ohm resistors to ground. I get 3.2v from each heater wire to ground .. 6.4v between the heater sides. Is this correct?
Any other ideas on a good place to start trying to make this thing work?
Thanks
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Welcome!
Look in here for a great way to double check the wiring on a new build;
http://el34world.com/Forum/index.php?topic=17701.0 (http://el34world.com/Forum/index.php?topic=17701.0)
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The diodes took a lot of heat from the soldering tip. Could one or more have been baked?
I think they're pretty sensitive to that, yes. I always clip a heat sink one when I'm soldering those. However, even 318 should be enough for making sound.
re: your heater CT. You don't have that grounded *and* have your artificial tap, correct? But yeah, 6'ish volts is right on the money.
As far as no sound, there's a mis-wire somewhere. I know for a fact it sure feels good when you find it!