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Dynakit ST70

MissionX said:
Off Topic: Are the American Made Tung Sol 6550's sought after? One of the bottles is
ZGHwie.jpg
cockeyed.
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Skewed bottles seemed the norm for Ts but they were technically good.
As far as value, depends on life test and other factors.
 
I bought the TungSol EL34B's as a matched quad from Jim McShane. They are great sounding tubes and at the time a great price
 
MissionX said:
Are the sound characteristics full bodied and more of mid to bottom or more on the bright side?
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Never found them to be bright at all just an excellent sounding well rounded tube. They compare well with the Japanese 6CA7's I have so full bodied would cover it. I use IC caps for restoring tube stereos because I like the sound so I know what I'm looking for and want out of an amp. With that constant it helps judging how a tube affects the sound
 
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Semi-off topic: I found the bottom end I was missing with my Mark III. I connected an 8 ohm A6 with an adjustable crossover instead of my 16 ohm A5 with a fixed crossover. I can dial it in so it's very pleasing. I think if I build or acquire an adjustable crossover for my A5's I'll be on the right track for what I'm looking for out of the more detailed A5's.

I'd say the A6's are for crankin' some hard rock or movies and the A5's are more for Pink Floyd, Supertramp, Eagles, Beatles.....they just need more on the bottom IMHO.


A6

A6

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A5

A5

  • Media owner MissionX
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MissionX said:
Are the sound characteristics full bodied and more of mid to bottom or more on the bright side?
Click to expand...
My only other EL34s are Chinese Nesstones which are very sweet with a soft top, somewhat flabby bass and a thick midrange. By comparison, the 6CA7s sound more neutral with an extended top end. Synergy.
 
Well I ordered the EH 6CA7's yesterday. I should have the rest of the parts soon. One of the resistors and one of the 82pF caps was out of limit.. Once I get her fired up I will do the updates.
 
I'm giving an ST-70 with EH EL34 a run currently. Honestly I don't have anything bad to say about these tubes. To be fair I haven't rolled any other tubes in here but I don't really feel the need to either.

This is a stock circuit ST-70, only change is 6GH8 in an adapter in place of the original 7199.
 
gadget73 said:
I'm giving an ST-70 with EH EL34 a run currently. Honestly I don't have anything bad to say about these tubes. To be fair I haven't rolled any other tubes in here but I don't really feel the need to either.

This is a stock circuit ST-70, only change is 6GH8 in an adapter in place of the original 7199.
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What are your impressions of the amp? Care to share?
 
I haven't spent a ton of time with it. Was running it a couple weeks ago but the can cap blew up. I was enjoying it then though.

New can is in, and its been run to verify its happy but I haven't actually had the time to just sit here and really listen to it to see if anything changed. Based on earlier impressions though, I get why people are into these things. It has no significant sonic signature, which I consider to be a plus. Its clean and detailed where you'd expect it to be without being so overly detailed that its fatiguing. I don't mean to damn it by faint praise, but I really just don't have anything bad to say about how it sounds.

Hopefully this week I'll have some time to just sit here and actually listen to it, and swap to the Pilot SA-260 so I can get a proper A/B of what should be comparable on paper amplifiers.
 
Finally received the rest of my capacitors today and fired my amp up. I'm quite pleased that it works! A couple of questions. 1)The capacitors I received today were to replace the 50uF 75V. I ordered 47uF 100V and figured I'd be good. One of the caps value measures 45uF and the other 40uF. I'm a bit disappointed since I waited 3 weeks for them due to some shipping anomalies, I'm told. I think I'm too far off on the 40uF..2)The right bias pot is maxed out to the anticlockwise side @ 1.6V. The left bias is in the lower part of the first quadrant and is adjusted @ 1.56V. I haven't done the updates yet, but I remember on the Mark III that I could change the value of the diode resistor and move the bias pot adjustment to the right or the left. Can I do a similar operation on this amp? TIA
 
40uf will be fine. The originals were probably at least 20% tolerance. Change those first before you do anything in the bias circuit. A bad first cap will make for low voltage and there isn't any point in modding things to compensate for bad parts. If that doesn't do it, replace the selenium bias rectifier if it hasn't been done already.

also I'm assuming if you turn the pots clockwise, the reading at the bias jacks goes up? Sometimes the pots get wired backwards, so just making sure its a case of not enough negative grid voltage rather than too much negative grid voltage.
 
After installing the diode, the pot was moved more towards neutral where I feel comfortable. I noticed in this amp there is a very slight hum in between songs as there is not in my Mark III. I replaced the electrolytic capacitors with 100uF 100V (because I had them already) and it made no difference. If this is normal, I'm not going to chase it. It's not objectionable, it's just there. My speakers are very efficient. Thanks

Edit: I haven't listened to it very long, but I already think it is softer than the Mark III, which I am happy about.
 
Well I've been enjoying my amp for a couple months now. I must have had "new car syndrome" referring to the hum. I don't hear anything unless I'm on top of it. If you've seen any of my other threads, I have the A5s with 515Bs and 288s crossed over with a modified Hiraga circuit and I'm liking it quite a lot.
 
Sounds like you are in good shape. Regarding the hum, I had a bad one unless I cheated the ground from the three prong cord I added when restoring it over two years go. Opening it up a few weeks ago I was alarmed to see a cold solder joint on the black OPT wire ground point. Once I got that fixed, the amp is dead silent, as it should be.
 
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