Hi i'm a newcomer to this forum and already i have a problem:) Below is a copy of the email I sent to Roy yesterday. After a very quick reply, I tried what he suggested, but no cigar. Anybody got any ideas?
I noticed from reading a few posts that the quad cap on a dynaco 70 is wired slightly different (to different values,symbols) than a Mk4 and I'm wondering if that might make a difference. Thanks, Gord
Hi Roy,
Last spring I bought a pair of Mk4 boards and parts plus a pair of can caps, the 80-40-30-20 from ce Manufacturing. Well I've finally got around to building them and here's my problem. I get a loud and I mean LOUD squawk out of my test speaker and an audible vibration in the output trans. I measure voltage on the speaker outputs of up to 50 VAC on the 16 ohm. Progressively less VAC on the 8 and 4 ohm. When I lift the feedback wire the squawk and the volts go away and the amp won't work when I put it in my system. I've checked voltages on the board and at the tubes, although not perfect, pretty close. I've also checked all resistors, wiring and soldering ( I rewired with silver plated multistrand 22 gauge). Also checked board caps and diode plus the multi can cap. Just now I swapped the output transformer for the other one. Same results, audible vibration in output transformer, squawk from speaker, high speaker terminal voltage. Do you have any suggestions or have you heard of this problem before? I'm a relative newcomer at this electronics thing, but i can follow directions.
Thanks,
Gord Wilson
I noticed from reading a few posts that the quad cap on a dynaco 70 is wired slightly different (to different values,symbols) than a Mk4 and I'm wondering if that might make a difference. Thanks, Gord
Hi Roy,
Last spring I bought a pair of Mk4 boards and parts plus a pair of can caps, the 80-40-30-20 from ce Manufacturing. Well I've finally got around to building them and here's my problem. I get a loud and I mean LOUD squawk out of my test speaker and an audible vibration in the output trans. I measure voltage on the speaker outputs of up to 50 VAC on the 16 ohm. Progressively less VAC on the 8 and 4 ohm. When I lift the feedback wire the squawk and the volts go away and the amp won't work when I put it in my system. I've checked voltages on the board and at the tubes, although not perfect, pretty close. I've also checked all resistors, wiring and soldering ( I rewired with silver plated multistrand 22 gauge). Also checked board caps and diode plus the multi can cap. Just now I swapped the output transformer for the other one. Same results, audible vibration in output transformer, squawk from speaker, high speaker terminal voltage. Do you have any suggestions or have you heard of this problem before? I'm a relative newcomer at this electronics thing, but i can follow directions.
Thanks,
Gord Wilson
I reversed the wires and all is well. Actually better than all well, fantastic! A VERY nice sounding amp. You guys have a winner with this mod.