I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.
+2
peterh
Dave_in_Va
6 posters
Dynaco ST-70 Series 3
Spoon- Posts : 3
Join date : 2020-09-29
Dave_in_Va- Posts : 443
Join date : 2013-04-02
Location : Mid. VA
I'm not familiar with your amp but I have a VTA ST 70 and tried Gold Lion KT 88's. The inexpensive Valve Art EL 34's that came with the amp sounded better.
(I eventually settled on NOS Mullard EL 34's).)
(I eventually settled on NOS Mullard EL 34's).)
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peterh
peterh- Posts : 1833
Join date : 2012-12-25
Location : gothenburg, sweden
As the critical grid resistor in ser III is 275k it's on the limit for KT77. There isSpoon wrote:I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.
a risk for current avalanche aka redplating if luck goes out.
https://frank.pocnet.net/sheets/084/k/KT77_GEC.pdf
KT88 on the other hand is well within limits:
https://frank.pocnet.net/sheets/084/k/KT88_GEC.pdf
As for filament current, KT77 draws 1.4A EL34 1.5 and KT88 1.6A
KT88 will then load the powertransformer with 400mA extra or 2.5w.
This seems like a small amount.
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rjpjnk- Posts : 262
Join date : 2018-07-18
Spoon wrote:I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.
I have the Series 3 as well and I think the OEM JJ E34L tubes sound great, but then I have only tried one other set so far for comparison, the Mullard reissue EL34. Are you looking for more power or just a different sound?
Spoon- Posts : 3
Join date : 2020-09-29
Just sound difference. I've read great things about the GL's.
rjpjnk- Posts : 262
Join date : 2018-07-18
Please report back with your impressions if you try them. Thanks!
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johprice- Posts : 7
Join date : 2022-01-31
Spoon wrote:I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.
Hello Spoon
I also have an ST-70 Series 3. Just wondered if you have found any different tubes that work well in yours?
johprice- Posts : 7
Join date : 2022-01-31
Has anyone found any different tubes that work well in the ST-70 Series 3? Mine has always seemed to bright and harsh with the factory installed tubes.
peterh- Posts : 1833
Join date : 2012-12-25
Location : gothenburg, sweden
Some distortion/power measurement could give some light on this.johprice wrote:Has anyone found any different tubes that work well in the ST-70 Series 3? Mine has always seemed to bright and harsh with the factory installed tubes.
Spoon- Posts : 3
Join date : 2020-09-29
I pretty much gave up on trying new tubes. Radial was no help. They basically said try what you want at your own risk. Really?
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
There is nothing inherently wrong with the Dynaco ST-70 Series 3.(Note - this amp is sometimes also called the Dynaco ST-70X) It looks nice and probably sounded good also. The problem is that Radial Engineering priced the amp too high at $3000 USD. At that price point, this amp had to compete with the USA made Rogue amps. I predicted that they would fail and that is exactly what happened. Sometime in early 2020, Radial Engineering pulled the plug on this amp. They just walked away from the amp, when they found out that the amp would not sell at $3000 USD. They finally sold the remaining amps in stock for $1499 and the amp quietly went away. Check out the post that I put up in 2015 and read the 5 pages of posts to find out about the history and demise of the Dynaco ST-70 Series 3. Link below ..
Dynaco Series 3 post from 2015
Bob
Dynaco Series 3 post from 2015
Bob
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johprice- Posts : 7
Join date : 2022-01-31
I will. Thanks Bob! Do you recommend any certain tubes for the Series 3?
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
johprice wrote:I will. Thanks Bob! Do you recommend any certain tubes for the Series 3?
You can probably use EL34, 6CA7, 6L6, KT66 and KT77 output tubes in that amp. The bias system is probably optimized for EL34's but the other tubes that I mentioned should work OK.
Bob
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johprice- Posts : 7
Join date : 2022-01-31
Spoon wrote:I pretty much gave up on trying new tubes. Radial was no help. They basically said try what you want at your own risk. Really?
That’s pretty lame of them. I was reading about the Gold Lions too. I’ll let you know if and when I try them.
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johprice- Posts : 7
Join date : 2022-01-31
The Series 3 or X model I purchased is very well built and, so far, sounds very good. I paid a little over $1200 for mine new in the box. A solid performer at that price. I would agree that $3000 is way out of line.
peterh- Posts : 1833
Join date : 2012-12-25
Location : gothenburg, sweden
ST70 series 3 has a grid resistor of 274k, that rules out KT66 . KT77 is a border case and
should probably be avoided. 6L6GC is also out as it needs a grid resistor of not more then
100k in fixed bias.
Why ? The answer is to keep the tube safe from redplating. Many times it will work, at least
with new tubes, but running with too large grid resistor is like playing with a dragon. It might hurt
and it's your own fault.
should probably be avoided. 6L6GC is also out as it needs a grid resistor of not more then
100k in fixed bias.
Why ? The answer is to keep the tube safe from redplating. Many times it will work, at least
with new tubes, but running with too large grid resistor is like playing with a dragon. It might hurt
and it's your own fault.
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johprice- Posts : 7
Join date : 2022-01-31
Bob Latino,
Do you recommend a certain brand of tube for the ST-70 Series 3?
NOS or newly produced tubes?
Do you recommend a certain brand of tube for the ST-70 Series 3?
NOS or newly produced tubes?
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