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Old 18th February 2011, 08:43 PM   #1
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Default St 35 or St 70?

I am going to build one of these kits. I have never built a hi-fi tube amp, but I have built many guitar amps. I have a couple of questions:

1. I dont usually listen to music very loudly. I am concerned that I will not be able to get the EL34's in the ST 70 loud enough to get them to their sweet spot. Is there any validity to this concern?

2. I have lots of guitar amps that use EL84's so I already have lots of NOS on hand. I dont have any access to good NOS EL 34's.

Aside from the issue if I will be able to take advantage of the EL 34 headroom, is there a difference in sound quality between the two kits?

Thanks,
Jon
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Old 18th February 2011, 09:18 PM   #2
eeyore is offline eeyore  Australia
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If you have lots of EL84 go with the ST35. It's still plenty of power and if you have speakers in the 90 dB range it should be loud enough. Some say the EL84 is a better sounding tube. I have a SET EL84 and the sound is fantastic.
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Old 18th February 2011, 10:23 PM   #3
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I'm no fan of the ST70, so if you don't need the extra power then go with the ST35. Output tubes are less inexpensive too.
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Old 18th February 2011, 10:41 PM   #4
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I'd go with the Stereo 35. The Z565 was a better output transformer than the A470. You say you've got plenty of spare 6BQ5. Honestly, even though the 70 is double the output power, it doesn't translate into that much additional headroom.
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Old 18th February 2011, 11:41 PM   #5
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Disclaimer > Many know that I sell an ST-70 amp kit so take that into consideration when reading below.

I disagree with the above three posters. The ST-70 is the way to go for the following reasons ..

1. The ST-70 has double the power of the ST-35 for only about $125 - $150 more money. With more power you have a wider selection of available speakers.

2. The ST-35 has no on/off switch unless you add one. (See link below.) Most users of ST-35's resort to plugging the amp into a switched outlet or a power strip which is a lot easier than plugging and unplugging the line cord into a wall outlet to turn the amp on.

3. The ST-35 can only use EL84 (or their Russian equivalent) output tubes while modern ST-70's built from kits can use EL34, 6L6, KT66, KT77, KT88 or 6550 output tubes.

4. A stock ST-35 has no adjustable bias system like the ST-70 although adjustable bias systems are available for the ST-35. (at extra cost > $65). With a stock ST-35 you put your four EL84 tubes in there and play the amp. As the output tubes wear a little you have no way of compensating for a problem tube.

That said, the ST-35 in stock form is a very good sounding amp. Certain mods can bring up the sound a notch though. See link below.

ST-35 mods link

Bob Latino
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Old 19th February 2011, 02:16 AM   #6
ArtG is offline ArtG  United States
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Disclaimer > I'm Biased. I own 3 ST-35s, and I love 'em!

...but I have high efficiency speakers, and that is a factor.

I have owned both, and they are both worthy of your consideration. Today's ST-70s have improvements in both circuit design and component quality that has probably narrowed the gap between them.

Below is another mods link that you should look at if you are considering the ST-35, or already own one..

Dave's Lab
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Old 19th February 2011, 05:22 AM   #7
rknize is offline rknize  United States
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I have what is essentially one of Bobs "VTA-70" kits. It addresses many of the ST-70 shortcomings and is a much more refined beast as a result. As others have suggesed, I would make your speaker sensitivity the driving factor of your choice.
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Old 19th February 2011, 06:06 AM   #8
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Quote:
Originally Posted by Bob01605 View Post
4. A stock ST-35 has no adjustable bias system like the ST-70 although adjustable bias systems are available for the ST-35. (at extra cost > $65). With a stock ST-35 you put your four EL84 tubes in there and play the amp. As the output tubes wear a little you have no way of compensating for a problem tube.
That gets into the whole fixed bias vrs cathode bias.

I currently have an EL34 PP, A complete rebuild using ST70 iron, with a Gregg-the-Geek DynaMutt front end. I rather like it. It trounced a 4k commercial offering i had on hand.

My next build thou will be a PP EL84 with cathode bias (i have chassis and a full set of dual mono ST35 iron). Why? We have a Class A triode EL84 based on El Cheapo with a Scott LK48 donor. Within its power limitations it sounds even better, I want to explore further what PP EL84 can do.

davewhat
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Old 19th February 2011, 07:35 AM   #9
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Quote:
1. I dont usually listen to music very loudly. I am concerned that I will not be able to get the EL34's in the ST 70 loud enough to get them to their sweet spot. Is there any validity to this concern?
As far as I'm concerned: no. That's more of a consideration from the guitar world, where the sound of overdriven power tubes is often regarded as desirable. In the world of hifi, audible distortion is usually frowned upon.
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Old 19th February 2011, 11:08 AM   #10
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I never used to be a fan of the Dynaco stereo 70 and I mentioned that here years ago. After playing with the 70 and finding out basically that you throw away everything except the power transformer and output transformers and then start over.

The "Geek" Dynamutt board is by far the best sounding Dynaco board out there. Use it and Geeks power supply board along with individual output tube bias and you will have a great sounding 70.

My second choice for a 70 driver board would be the "Mapletree Driver Board". After that there are a number of ok sounding boards. The board that "Bob" pushes doesn't sound too bad but I personally feel the high end is a little exaggerated.

The Triode board that uses a 6AU6/12au7 combo is a nice sounding board at a reasonable price.

Basically the 70 suffers from a junk driver board and an anemic power supply.
You don't have to use expensive EL34's to make it sound good either. A cheap set of 6BG6GA's ( again a thanks to SY for the 6BG6GA tip) or Russian
6N3C-E tubes and it will sound great.

Last edited by Original Burnedfingers; 19th February 2011 at 11:17 AM.
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