Dynaco ST 70

[TubesGlo]

I refreshed my 70 leaving only the transformers and chassis as original. After reading Gillespies Base Line Test I decided to keep the stock circuit using Dynakitparts factory replacement board. I have 3 sets of strong testing 7199's. I also have 2 full sets of Mullard xf2's all testing good and strong.
However... I decided to try the NOS Russian surplus 6p3s-e and I haven't gone back to the EL34'S. I did tweak the resistors in the bias circuit for better range. I'd be hard pressed to find a quad of current production tubes for 90 bucks that sound this good and they sure as hell won't last as long. These things sound friggin' awesome. More detail up top and tighter lows. I know guys started getting turned on to these more than 10 years ago but I was late to the game.

 

[TubesGlo]

I had those many years ago and liked them. Still using the Chinese Nesstones and they are doing well, but I should do something else.
I will say that an updated ST-70 using the stock circuit is a very good amp. Although there are surely better amps available, I am content.

I did alot of research before restoring my amp and after a couple back and forth emails with Dave G. I was convinced that keeping the stock circuit was the way I wanted to go. I know plenty have gone with VTA boards but in my mind it becomes a completely different amp with a different sonic signature. Better, worse I don't know but my amp with Takman carbon films and PIO coupling caps and 7199's sounds pretty excellent with my Cornwall Clones.

 

[Blackdog61]

I refreshed my 70 leaving only the transformers and chassis as original. After reading Gillespies Base Line Test I decided to keep the stock circuit using Dynakitparts factory replacement board. I have 3 sets of strong testing 7199's. I also have 2 full sets of Mullard xf2's all testing good and strong.
However... I decided to try the NOS Russian surplus 6p3s-e and I haven't gone back to the EL34'S. I did tweak the resistors in the bias circuit for better range. I'd be hard pressed to find a quad of current production tubes for 90 bucks that sound this good and they sure as hell won't last as long. These things sound friggin' awesome. More detail up top and tighter lows. I know guys started getting turned on to these more than 10 years ago but I was late to the game.
View attachment 2678068

Interesting idea on those. I looked into those as well as 6L6 and 5881 options but they all seemed yo have a plate voltage of about 250 and my ST-70 runs about 430. Thoughts? I have a few to try but never had the guts to.

 

[Lavane]

I personally wouldn't run 6L6's or 5881's in a ST-70. 5881's maybe if they were
Old stock Tung Sol?

 

[peterh]

I refreshed my 70 leaving only the transformers and chassis as original. After reading Gillespies Base Line Test I decided to keep the stock circuit using Dynakitparts factory replacement board. I have 3 sets of strong testing 7199's. I also have 2 full sets of Mullard xf2's all testing good and strong.
However... I decided to try the NOS Russian surplus 6p3s-e and I haven't gone back to the EL34'S. I did tweak the resistors in the bias circuit for better range. I'd be hard pressed to find a quad of current production tubes for 90 bucks that sound this good and they sure as hell won't last as long. These things sound friggin' awesome. More detail up top and tighter lows. I know guys started getting turned on to these more than 10 years ago but I was late to the game.
View attachment 2678068

Any figures that supports the claim ? Measurment etc

 

[TubesGlo]

Any figures that supports the claim ? Measurment etc

There's plenty of references on forums where these tubes have been used successfully. Jim McShane was selling these 12 or so years ago burning them in while testing at upwards of 500v on the plates without issue. He recommended following the spec sheet for the 6l6gc. Now this is only for the 6p3s-e
(6n3c-e) with the coin base. These are extreme duty mil spec tubes vs the non e civilian version where the max plate voltage is indeed only 250v. I've been running my tubes at 410-420v on the plate 4 hours a day on average every day for 4 months. Google 6p3s-e and 6n3c-e ST-70, plenty of info.

 

[TubesGlo]

I personally wouldn't run 6L6's or 5881's in a ST-70. 5881's maybe if they were
Old stock Tung Sol?

You're missing out. McShane told me the current production Tung Sol 6l6gc is an excellent tube. I agree though, standard issue 6l6 or 5881 can't handle the plate current but those current Tung Sol and TAD 6l6gc str certainly can. These NOS military spec 6n3c-e are less expensive and bomb proof...literally plus they sound incredible. I'm sitting on 2 quads each closely matched xf2's that were my pride and joy and although I really hate admitting it, these 6n3c-e 's do sound better. I have 100db sensitive Cornscala's with the amp in Triode mode and the speakers on the 4ohm tap.

 

[TubesGlo]

Wasn't sure how to link it but this is one thread from AK

 

[Lavane]

You're missing out. McShane told me the current production Tung Sol 6l6gc is an excellent tube. I agree though, standard issue 6l6 or 5881 can't handle the plate current but those current Tung Sol and TAD 6l6gc str certainly can. These NOS military spec 6n3c-e are less expensive and bomb proof...literally plus they sound incredible. I'm sitting on 2 quads each closely matched xf2's that were my pride and joy and although I really hate admitting it, these 6n3c-e 's do sound better. I have 100db sensitive Cornscala's with the amp in Triode mode and the speakers on the 4ohm tap.

I bought a matched quad of the same Russian tubes for a Russian made guitar amp I restored for my son. Nice tubes.

 

[peterh]

There's plenty of references on forums where these tubes have been used successfully. Jim McShane was selling these 12 or so years ago burning them in while testing at upwards of 500v on the plates without issue. He recommended following the spec sheet for the 6l6gc. Now this is only for the 6p3s-e
(6n3c-e) with the coin base. These are extreme duty mil spec tubes vs the non e civilian version where the max plate voltage is indeed only 250v. I've been running my tubes at 410-420v on the plate 4 hours a day on average every day for 4 months. Google 6p3s-e and 6n3c-e ST-70, plenty of info.

Ok.
What is the values for distortion and power in contrast to EL34 ?

 

[TubesGlo]

Ok.
What is the values for distortion and power in contrast to EL34 ?

Not sure of distortion specs but I can tell you if there is any it's inaudible. They're clean sounding, open and airy, detail with what to me sounds like better extension at the high and low end of the spectrum. I believe the power output is a little less than the xf2's but I'm running in triode so for me it's less anyway. However with my speakers the first couple of watts is all that matters anyway. I get 85- 95db without the amp breaking a sweat, effortless. I don't have more than my God given ears for test instruments and I trust them. Believe me, I never thought I'd set my xf2's aside. These tubes are that good. I'd suggest checking out the many comments and threads on the internet that make the same claims.

 

[vitorzoom]

Hello everybody! Sorry for the delay in thanking everyone, but I had a lot of work commitments and now I'm back.
Last night I was listening again and I still have a great impression of the amplifier.
I will try to find some of the suggested valves.
But this amp reduced the aggressiveness of the Yamaha ns 1000 in the mids and highs. I can listen longer without hearing fatigue.
But it's all very new to me. Maybe with better valves I can improve a little what is already good.
Thank you all for the goodwill.

 

[Lavane]

You're missing out. McShane told me the current production Tung Sol 6l6gc is an excellent tube. I agree though, standard issue 6l6 or 5881 can't handle the plate current but those current Tung Sol and TAD 6l6gc str certainly can. These NOS military spec 6n3c-e are less expensive and bomb proof...literally plus they sound incredible. I'm sitting on 2 quads each closely matched xf2's that were my pride and joy and although I really hate admitting it, these 6n3c-e 's do sound better. I have 100db sensitive Cornscala's with the amp in Triode mode and the speakers on the 4ohm tap.

I have a quad of strong old stock Tung Sol 5881's. I wish they were better matched. Two of the four are pretty close though. Inhave thought about trying them in my VTA ST-70. Supposedly they can handle the higher voltage.

 

[gadget73]

I tried a set of 6P3S-E tubes in my Pilot SA-260. I found it to be overly bright and "brittle" sounding, and thats an amp that tends to have a noticeably rolled-off top end. I think I got through one song and had to shut it off because it sounded so obnoxious. I put the EH 6CA7 tubes back in it and that was the end of that.

 

[peterh]

Hello everybody! Sorry for the delay in thanking everyone, but I had a lot of work commitments and now I'm back.
Last night I was listening again and I still have a great impression of the amplifier.
I will try to find some of the suggested valves.
But this amp reduced the aggressiveness of the Yamaha ns 1000 in the mids and highs. I can listen longer without hearing fatigue.
But it's all very new to me. Maybe with better valves I can improve a little what is already good.
Thank you all for the goodwill.

Make sure the tubes at each side is truly matched. Purchasing a matched quad will ensure you still
have at least 2 matched tubes even if any 2 fails in the future.
True matching ( at high voltage) is more important then tube brand or price.

 

[TubesGlo]

I tried a set of 6P3S-E tubes in my Pilot SA-260. I found it to be overly bright and "brittle" sounding, and thats an amp that tends to have a noticeably rolled-off top end. I think I got through one song and had to shut it off because it sounded so obnoxious. I put the EH 6CA7 tubes back in it and that was the end of that.

Quite the opposite for me in my ST-70. My tube preamp has PIO output caps, amp has PIO coupling and speaker crossovers PIO caps. I notice better detail and extension top to bottom from the 6n3c-e, not "bright at all. I suppose any output tube may sound different in a different circuit. These particular tubes do take a little time to get into their sweet spot. I've gone back to my xf2's a couple of times and pull them after the 1st listening session in favor of these. I suppose it's time to put them up for sale.

 

[TubesGlo]

I have a quad of strong old stock Tung Sol 5881's. I wish they were better matched. Two of the four are pretty close though. Inhave thought about trying them in my VTA ST-70. Supposedly they can handle the higher voltage.

Data sheet shows 400v max on the plate so you'd be right on the edge. Worth giving it a try anyway.

 

[vitorzoom]

Make sure the tubes at each side is truly matched. Purchasing a matched quad will ensure you still
have at least 2 matched tubes even if any 2 fails in the future.
True matching ( at high voltage) is more important then tube brand or price.

 

[vitorzoom]

Important to know that the "match between the tubes" is more important than a brand or value. As is completely new to Tube Audio. Thanks

 

[Blackdog61]

@TubesGlo sent me some Groove Tubes EL34Ms to try which are supposedly based on Mullard Xf2s. Replacing the Nesstones I immediately noticed more detail and a slightly forward upper midrange. I find the Nesstones to be more musical in my system. I’ve had a quad of EH 6CA7s for at least two years and eventually found them to be a bit harsh on top with my Canton monitors. The excellent bass they have was never heard by me with those speakers so they got pulled.
Well, several months ago I got some Vandersteens and finally decided to try those fat tubes. Now I hear it! The bass is much deeper and flatter; really the frequency response seems much flatter and the soundstage is wider and deeper. The top end is very smooth and detailed.
Component matching is SO important.
Waiting on some skinny RFTs next.

Also, I have been using 6GH8As with adapters on the Dynakit Parts 7199 board and ordered the 6GH8A board. I feel like that will complete the amp.