Masco tube amp

[Peter Blair]

Hi again Roly,
Thanks for the extremely clear explanation. I see I had it bass-ackwards.

Quote from: Roly

    For reference, a way of testing a coupling cap for leakage is to lift the grid end and measure the voltage between the free end and ground.  A good cap will eventually charge up and read zero volts, or something very close, while a leaky cap will show a residual voltage (which in the case of some waxed paper caps may be close to HT)

Just for an exercise, I think I'll test some of the coupling caps as you describe here. I'm just waiting for my parts order to arrive, so it will give me something to do that will definitely embed the whole idea in my memory. You are gifted with being able to communicate with the uneducated, in a way that make the topic at hand seem very clear. Where do I sign up for classes? I suppose right now, my best classroom is my workbench.

I will be reporting back after I've completed at least some of the repair.
Thanks again Roly,
Pete

[Peter Blair]

First of all, I want to say thank you all again for all your support. I've been ill for a while, so all my projects have been on hold for several months. Sorry if you've been waiting on hearing back for a progress report.

I finally did replace all the caps and the not-so-few resistors that didn't quite make the cut, spec-wise. Replaced the 6L6's with 6L6GTs. Turned out one of the tubes had an internal short. I know the schematic says GT's, but the chassis says 6L6s. I did this mostly to save cost. This did require quite a change in the bias resistor to get things to a reasonable plate dissipation, but I'm pretty sure I've got it right. I went over all the spec's several times. I'm not writing back to burden anyone with further analysis or information. I just wanted you to know that I did eventually follow through and got it done, thanks in great part to everyone's help and generosity. The amp does sound pretty good, although it does seem to break up a little early. Bear in mind, this amp is sought after by harp players BECAUSE it breaks up nicely. Gives the sound they want. So I'm marking the whole thing up as a win.

I'll be reading the forum regularly to see what I can learn just by eavesdropping. If I need help on something again, I'm hoping you'll all have a little bit more patience left for me.

Pete