Finally a tube amp!!

[roccus]

I have this Dynakit ST70 it was dead when I got it so I dug into it and got it up and running, sounding good but needs at least new tubes. Plan for this is to drive my Altec HF horns, may do some upgrading on it first. Next on my plate is to get the pl400 up and running. I had bought a pl400 bare chassis that only had the transformer on it to build a wopl 400 but I needed meters for it so I grabbed a 400 off fleabay for the meters. Well when it got here it was just to nice of a 400 to gut and it ran well. Soo I bought another 400 and used it for the meters. But that 400 ended up cooking the left channel. I think I want to get it running to drive my Altec mid cabs. Think I will put a WO control board and upgraded power caps in but not sure about the back planes....

 

[George S.]

That's really nice. A true survivor.

 

[marcok]

It sounds ,it sounds great |
I have a VTA ST 70 and I'm very happy !
Anyway I have seen that you have already replaced caps on the driver board
and that you probably have inserted a volume control instead mono stereo switch .
Replace ,unless you have already done , the quad cap .
J&J are good tubes , but , unfortunately driver tubes (7199 ) are discontinued .
Enjoy music !
Ciao
Marco

 

[mr_rye89]

I had one last year, retubed with Ruskie Mullards. It had a Rubycon multi section electrolytic capacitor that was still good, but I replaced the rest of them including those domino looking ones because those are molded paper types (and bombs!) There’s also adapters to change the 7199s to 6GH8s but don’t cuz I hoarded all those for my TV

 

[roccus]

It sounds ,it sounds great |
I have a VTA ST 70 and I'm very happy !
Anyway I have seen that you have already replaced caps on the driver board
and that you probably have inserted a volume control instead mono stereo switch .
Replace ,unless you have already done , the quad cap .
J&J are good tubes , but , unfortunately driver tubes (7199 ) are discontinued .
Enjoy music !
Ciao
Marco

I am going to replace the control board have ot made up my mind yet which one I will go with but one that uses the 6GH8 tubes. I did not put that voume control on it came with it I might get rid of it, I did replace the quad cap from one I got from Dynakit as well as the power supply caps I got from digikey

 

[roccus]

I had one last year, retubed with Ruskie Mullards. It had a Rubycon multi section electrolytic capacitor that was still good, but I replaced the rest of them including those domino looking ones because those are molded paper types (and bombs!) There’s also adapters to change the 7199s to 6GH8s but don’t cuz I hoarded all those for my TV

Not sure which EL 34's I will go with I have read either the russian mulards and the JJ's go real well in these I'm going to do a board conversion so I can just plug the 6GH8 tubes in without using adapters to run 7199s that are crazy prices for them can replace the board and a couple 6GH8's for the price of a set of 7199's

 

[roccus]

On the board I am leaning with the one that uses 3 6GH8 tubes and eliminates the original selenium rectifier

 

[mr_rye89]

6GH8s are also out of production, and you probably don’t need to splurge on fancy US made RCAs to use as a driver because the Dynaco doesn’t run them at their operational limits like color TVs do. If I was going the driver board replacement route I’d get something that uses 6DJ8s or 12BH7s, but that’s just my opinion.

 

[marcok]

My opinion Is :
- Replace only the EL 34 s , the rectifier GZ 34 and the quad cap .
Replacing the driver board with a 3 tube type ( 12AX7 ) means
redesign "everything ". My Vta ST 70 has a more powerful transformer
and another choke and so on .
Ciao
Marco

 

[Skratch]

Triode Electronics in Chicago has everything you will need to upgrade your Dynaco

 

[roccus]

My opinion Is :
- Replace only the EL 34 s , the rectifier GZ 34 and the quad cap .
Replacing the driver board with a 3 tube type ( 12AX7 ) means
redesign "everything ". My Vta ST 70 has a more powerful transformer
and another choke and so on .
Ciao
Marco

Going to stick to a 2 tube 6GH8A type board upgrade and I think the selenium rectifier replace/upgrade kit.. this amp is going to be used to drive my altec HF horns, they don't need much power so this amp will not be working very hard, maybe replace the RCA input jacks with new and add binding posts for the speaker connections.... right now it is limping along ok connected to my old bose 301 speakers and PL 3000 pre amp

 

[roccus]

6GH8s are also out of production, and you probably don’t need to splurge on fancy US made RCAs to use as a driver because the Dynaco doesn’t run them at their operational limits like color TVs do. If I was going the driver board replacement route I’d get something that uses 6DJ8s or 12BH7s, but that’s just my opinion.

I have a couple sets of nos RCA 6GH8A's on hand from back when I used to do jukebox amps