|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
69.134.190.5
In Reply to: Re: Looks like we got a preamp problem... posted by groverg on December 26, 2004 at 17:21:28:
I believe the output cap is 1.0 mfd/400vdc. The specs on the power tranny are 1206vct/0.35A.
I was just reading through your suggestions and realized that I use relay sockets on my breab board. Is there any way I can hook up the grid stoppers on those and have it still work?
I really appreaciate all the help Grover!
Vince
Follow Ups:
It wouldn't hurt to tie one to the relay terminals. Let me know when you get back to it.
Good morning Grover. I have today and Friday off due to the holidays, so I am taking vacation leave for the rest of the week to try and get some remodeling done around the house.
I tried the grid stopper just a short while ago. I put a 1k resistor to pin 4 of the 6n7 and attached the input wire to the other end. I kept the end on the relay short by doubling over the lead and sliping it under the clamp. Pins 4 & 5 are tied together with a short lead. They don't need separate resistors do they? I left the bypass cap for the cathode resistor of the 6n7 out, but the preamp was in.
Well, it went about 12 minutes this time before it went pop and stopped playing. Does this mean we are making progress? What do you think I should try next?
What was your take on the output cap of the preamp and the specs of the PS tranny?
Thanks!
Vince
The power tranny and the output cap would appear to be fine. The power tranny may be buzzing because you're powering it off the variac. We'll look into that more later.Here's what I would do next:
Restore the bypass cap to the 6N7. Make sure the 6N7 is wired properly--you have 4 & 5 tied for the grids, and you should have 3 & 6 tied for the plates, and 8 for the cathode resistor.
Disconnect your preamp from the amp, turn it on and make sure you don't have any measurable DC from the output to ground. A leaky output cap could cause the problem you're having.
Is there any way you can place a volume pot at the input of the amp (anything from 25-200K would suffice) and test the amp with your CD player or source directly inputted? That would tell us a lot.
Just so happens my bread board is semi permanent and has volume pots built in for each channel. I will first check the preamp for a leaky cap and then I will put the bypass cap back in and run the cd player directly into the amp. I just checked the wiring on the 6n7 and it is correct. I will get back to you as soon as I do these things.
Vince
This post is made possible by the generous support of people like you and our sponsors: