Tube Amp Archive

I have 12A in their right now but something is not right. I can conect the input directly to the pin volume pot and have decent sound, but my V1a voltages are way off. My V1a plate voltage is around 300 vdc. I dont get anything when I connect to the input of the 68K R, so I thik I have a V1a problem...

thanks the input - I will double check the soldering today. Originally I thought it had something to do with the OEM jack, which according to the schematic has 4 connections(?!) and my replacement has 3. Nothing I put at the junctiona of that 1 meg and 68K resistor causes any sound....so will check ...

I'm finishing up a Fender Champ II, ready to wrap it up, but I only get signal when I connect to the volume pot, not the 68K input resistor. It sounds OK, voltages are fine etc., but without anything connected to 68K input resistor. The schematic shows the input jack with 2 connections - 1 to the vo...

I have finished building a clone Fender Champ II - it works but only by sidestepping the normal input and jacking into the 250 pFd cap. I'm trying to find one of these 4 pin jacks but was wondering if there was another way to handle this with a standard Switchcraft? The amp seems to work OK, still t...

The .02 are both 630 volt orange drops - I just tried swapping to no avail. the 6V6 cathode resistor is only 1/2 watt - I will replace that. I did pull up one leg and check the value. Also checked the value of the 220K and the 100K resistors....I'm running out of things to check...I'm about to take ...

aha - ok will do - and let you know....

At first it was as original - then as I noticed problems, I switched over to floating 6.3 vac heater and ungrounded the other end of the 6.3 vac tap (I had done this on a previous Champ II)...so now is 6.3 volts toeach side of the heaters and on to the power indicator

Here are some fresh measurements with tubes installed. Now that I've caught on to the fact that the voltages go south as it warms up it is quite pronounced so I include two measurements. Quiescent, or at power-up and as it warms up and starts delivering static. Then the tubes tart operating and some...

I will go back and do new tube measurements. And I did get rid of the "death cap". The 6V6 appears to be operating normally - not red-plating. and all-in all it sounds like it's trying to work...I did find a wire that came loose on the bottom on the first inspection and will re-check the grounds. Th...

And the plot thickens - I noticed that the B+ volts age drops from 395ish to 330 as the tubes warm up and the B+ stays high when I pull the preamp tube...so it seems like it's somewhere in there - I did swap out a 7025 but will do it again... It does amplify to some extent but just isn't loud as I t...

yes - that .4 v was out of circuit - in circuit the 6V6 cathode voltage is 25.7 vdc. I meant to include as the measured voltage. And yes - if I pull the 7025, the B+ stays up at 395... I screwed up in the image URL - here is the thing...I populated the board with parts I purchased...Yes I thought th...

I just built a 5F1 and powered it up and it kind of amplifies but mostly pops and sounds like static on an old shortwave radio. The B+ voltages seem to be low (336 vdc), but pop back up (395 vdc) when I take the tubes out. I originally suspected leaky caps and so have replaced all of the electrolyti...