Tube Amp Archive

Another vote for conductive boards. Since both amps have similar fiberboards I think that's more likely the issue than them both having faulty tubes, but the tubes are easy to rule out. If you probe around on the circuit board with a probe to ground, can you get voltage readings? I mean from the fi...

Did Fender make that change in the BF amps to allieviate that issue? IOW, was DC leakage on the input a common enough problem with tweeds that they changed that? No and no. DC leakage was not a problem with the new boards that Fender used. But it became a common problem years later when the boards ...

So.. short of scrapping the boards and rebuilding them, is the "adding a cap to the input" a decent way to filter out that DC? If so, just a .047 from tip to ground on one input the way to go? Or in line with the wire going from the tip to the grid stoppers? You would need two caps since you have t...

More info... I misspoke when I said there was no voltage on the boards. 5f2a: tip to sleeve input 1: 59.8mV Board to ground: 16mV TweedleDee: tip to sleeve input 1 Bright channel: 179mV Board to ground: 41mV So yeah, there is voltage on the boards. I did not build the TweedleDee so I don't know who ...

What material did you use for the circuit board? CW It's the stock fiberboard that came with the kit. Same with the tweedledee that's fiberboard as well. Not getting voltage on either board. No voltage, zero volts anywhere on the board? That isn't even possible with vulcanized fiberboard. There is ...

It is odd you're getting DC on the input, as both go directly to the grid of the tube, i.e. no DC voltage present that can get to the input? It is known that some 12A?7 tubes can leak DC to the grid. You can try swapping V1 tubes to see if it makes any difference. This has happened to me. swapped o...

Hi, I have these to amps. When using either, the controls on any guitar are scratchy. I checked the input jacks and noticed that there is a little DC voltage present on the input jacks. If there is a buffer in the chain, the scratchiness goes away. As both of these are recent builds (I built the 5f...

Stevem wrote: ↑Mon Sep 21, 2020 4:27 pm Get a .47 200 volt cap and place it in series off of the hot of the input jack, issue over and if the amp does not have a grounded power cable you will be safe from getting shocks due to that also as a side benefit.

the cap from tip to ground?

Hi, I have these to amps. When using either, the controls on any guitar are scratchy. I checked the input jacks and noticed that there is a little DC voltage present on the input jacks. If there is a buffer in the chain, the scratchiness goes away. As both of these are recent builds (I built the 5f2...

The schematic says blue to pin 3. They layout shows red to pin 3. The finished chassis pic shows blue to pin 3 as well. Maybe Heyboer is inconsistent in their wiring? I definitely had a wiring problem I inadvertently fixed, then I had to put red to pin 3. But hey it was my first time and I learned a...

Ok. This is all sorted out. Pulled the negative feedback and the whistle disappeared. Swapped the IT wires so red is in pin 3 and I'm good to go. I had moved blue to pin 3 since those pix were taken.
The is for your help!

It looks more like that now. I've rerouted some stuff @ the 12ax7 and replaced the neg feedback wire as that was a little too short.

swapping the red and blue fixed the signal issue. Now there is guitar coming out of the speakers. There is a slight whistle that changes when the volume is turned up and when playing the guitar, there is a nasty distortion happening.
Here's a couple of videos.

I saw that, but I was under the impression that if those OT wires were reversed there would be a squeal. As it stands, there is no sound at all. No hiss, no pops when checking voltages etc.

More pics: