converting Heathkit AA-191 to a guitar amp

[Rich Wolski]

Hello one and all. I apologize profusely if this question is either hackneyed or trivial.

I am (as a first project in what I hope is a long list of projects) attempting to convert a Heathkit AA-191 into a charming, if demure, 3-watt guitar amp. I've fixed a grounding problem, and now I'm experiencing what I believe Jasniewski refers to as "pumping" in his article on converting tube PA and Hi-fi amps to guitar amps. I've wired the input jack to the phono input (just to be clear).

Having nosed around on the web a bit, a colleague of mine and I discovered that, perhaps, the voltage level from the guitar is too large and too dynamically fluctuating for the tiny Heathkit's circuit. We also found an article that described how to build a small passive RC filter that matched the guitar output to the amp input and some recommended values for the resistor and capacitor. Alas, we can't seem to locate the article again.

Any advice and/or pointers you can provide will be tremendously appreciated. I expect that this problem is the first of many we will encounter.

Cheers,

Rich

 

[SHiFTY]

It should be fine. Try reducing the coupling capacitor to the output tube to 0.047 uF if it is oscillating. Try also 1K grid stoppers on the EL84 grid, and a grid stopper on the EF86 grid.

Also you could try wiring the EF86 as a triode.