Dynakit Stereo 70 Stopped Audio Out

Hey Forum! Hope you're all well!

I have a Dynakit Stereo 70 Amp and Pre. I was listening to a record and the sound stopped. I was out of the room when it happened so not didn't see anything or hear anything funny, just came in and the record was going and there was no sound. Power is working on both. Tubes appear to be working on both. I tried an alternate (line-in) input and that's not working either.

I've gotten ok at tube replacement and bias work and i'm pretty good as a troubleshooter in general but my experience with analogue audio repair is pretty much non-existant in terms of replacing other parts.

Do you have any suggestions in terms of how to narrow down the problem further or steps I may have overlooked?

Thanks so much for you help. This system is crucial to my life!

David

tndave123 wrote:Hey Forum! Hope you're all well!

I have a Dynakit Stereo 70 Amp and Pre. I was listening to a record and the sound stopped. I was out of the room when it happened so not didn't see anything or hear anything funny, just came in and the record was going and there was no sound. Power is working on both. Tubes appear to be working on both. I tried an alternate (line-in) input and that's not working either.

I've gotten ok at tube replacement and bias work and i'm pretty good as a troubleshooter in general but my experience with analogue audio repair is pretty much non-existant in terms of replacing other parts.

Do you have any suggestions in terms of how to narrow down the problem further or steps I may have overlooked?

Thanks so much for you help. This system is crucial to my life!

David

You mention "AMP and PRE".
You could pinpoint if the fault is at the pre ( what brand is it ?) or the ST70 by
loosing the input cables to the st70. A large hum will sound if the ST70 is ok . If nothing
is heard then the st70 is at fault. Try the mains fuse first !

Hi Peter.

Thanks so much for the help.

The preamp / receiver are both Dynakit. My father put it all together back in 62. I tried loosening the inputs on the amp and the pre and didn't get a hum.





I removed the amp fuse and it looks good.

David

By loosening inputs i mean to slightly pull the front located inputs on the st70, just so much that the
circumference ground connection is lost.

If this wont cause large hum then the ST70 is dead.
Get the dynaco manual ( or you already have it ) it has a fault finding section that will be of value.
A good guess is the rectifier tube, but still a guess.
You will need a decent voltmeter and VERY CAREFUL fingers when measuring the voltages in the amp.
You should not be alone doing this as voltages are lethal inside. If in doubt do take it to
a repair shop.

Thank you so much everyone! I do have a person here in Brooklyn who does some basic repair. I'll try and check the rectifier tube / bias as you mentioned Bob. Probably will take it to someone if it gets beyond that.

Hi Bob.

Thanks for your help. I only get bias voltage from one channel. when i switch the small tubes by the bias checking area, the voltage moves with the tube. Do you think that might mean it's one of the small tubes (I think the 7199s?). I did replace the rectifier tube once a year or two ago and i did have to move the amp in the last few month (up a 4 story walkup which was no picnic).

Also, others have mentioned that my amp looks bad and I'm willing to have it professionally refurbed, just not sure where to take it. I'm in Brooklyn.

Much appreciated.
David

Also, one of the 7199 flashes whenever i turn on the stereo and I thought it was weird, but it always worked and there was no hum, so I thought maybe it was ok.

Thank you Peter. I'll take a look. I'm not terribly bad with putting things together with instructions and things like that, however I have developed a tendency to let professionals do work when i really want something done right the first time. In this case, because I rely on listening to records so much, I'd probably prefer to have someone do the work. With something like this I'll almost always make a mistake and I don't really plan on becoming an audio repair person, as neat as it seems. I'm afraid i'll shock myself to death actually. So, tubes, bias, fuse I feel cool with. Soldering, caps, things like that feel dangerous.

Hi all, Just fyi. I had Blackie Pagano work on the amp. It looks beautiful and is working perfectly.

What was the fix action?

Dean

Dynaco ST70...curve trace test all tubes for spec and replace as necessary.
Clean and tighten all pots, connectors, switches and tube sockets. Replace
intermittent power switch. Replace brittle power cable. Replace leaking film
caps with polyester film and foil vintage audio type. Connect previously
replaced power supply cap to ground with soldered wire connection. Check
bias and bench / playing test to spec all functions. Burn-in 45 min full power,
idle 4 hours, and recheck voltages, power output, functions and playing test.
Test large quantity of used tubes and supply test results.

also new tubes

He pretty much rebuilt it, should last a long time!

Dean