My rebuilt ST70s.

Very nice job!

Here's the evolution of mine...



started out with a pretty clean, stock example.
changed out the selenium rectifier, bias caps under the chassis, and installed SDS labs rca jack.




Switched to SED winged C EL34s. Installed new can cap and changed out the coupling caps to Solens.





Finally, replaced all resistors on the original driver board, and switched to Philips JAN 6U8A via sockets adapters.



Sounds very clean. My only regret was selling those original RCA fat bottles on eBay. They were very warm and meaty in the bass.

- Sushimaster

sushimaster wrote:Very nice job!

Here's the evolution of mine...


started out with a pretty clean, stock example.
changed out the selenium rectifier, bias caps under the chassis, and installed SDS labs rca jack.



Switched to SED winged C EL34s. Installed new can cap and changed out the coupling caps to Solens.


Finally, replaced all resistors on the original driver board, and switched to Philips JAN 6U8A via sockets adapters.


Sounds very clean. My only regret was selling those original RCA fat bottles on eBay. They were very warm and meaty in the bass.

- Sushimaster

Nice job, Sushimaster. Have you thought about swapping the tubes and caps? Playing with those 6U8A will make a huge difference. I also find Solen caps a bit too harsh too. I'd suggest Mundorf Supreme caps instead. I love them in my rebuilt Jolida JD801A.

ViperZ, I have tried Svetlana from New Sensor...didn't like them much.
I do very much like these SED winged C's. They sound very clear, clean.
I might try the new Mullards from New Sensor down the road. I haven't thought of Mundorf Supreme, but I might try new coupling caps in my next ST70 restoration.
Thanks for the recommendation.

- Sushimaster

BTW, Has anyone here tried the Electro Harmonix 6CA7 tubes in a ST70? If so what are your impressions of them?
Thanks.

- Sushimaster

sushimaster wrote:BTW, Has anyone here tried the Electro Harmonix 6CA7 tubes in a ST70? If so what are your impressions of them?
Thanks.

- Sushimaster

I have used EH 6CA7's on and off for over a year, I purchased a matched quad from The Tube Store dot com. These tubes sound deeper than El-34's and less warm. I would describe them as being more accurate than El-34's. They sound closer to 6L6 tube types as they are a beam tetrode rather than a true pentode like the EL-34. After about 300 hours I had one of the quad begin to draw much more current than it should have, so I bought another to replace it and they have been fine since then with about 1000 hours on them, give or take. They do look quite nice and have more visual presence than El-34's if you care about that sort of thing. I would recommend them if you want to try a tube that will sound significantly different in the ST70. Just be careful who you buy them from. Doug's Tubes does a full burn in of all their tubes and I have been pleased with everything I've purchased from them. I should also note that early models of this tube are known to have grid alignment issues, so look for ones that were made in the last 2 years.

Thanks for the review kevco. I think I will give them a try based on your recommendation.

- Sushimaster

Hello all you folks.
Glad to find so many fans of Dynaco. Am just now contemplating rebuilding a pair of very neglected MK 111's and wish to know how to test the transformers. Any help? These amps were sitting in a garbage bin, and ready to go out the door, so I thought I better pick 'em up. Too bad the Mullards' were spent!


thanks,
lostclockmaker