Another ST-70 question

[organ]

OK, here's another question for the ST-70 experts. My ASL is messed up right now and found an ASL repair center not too far away that will fix the problem and perform internal mods. The mods will run me about $160CDN which isn't bad and he said there's a big improvement over the stock version. After talking about the ASL with the technician, somehow we started talking about the ST-70. He told me that he had worked on many ST-70 and didn't recommend I keep it stock for the restoration. He said that the 7199's need to go. He said the best mod was one provided by Audio Research many years ago but I can't find it anywhere. Anyway, the person who's going to restore it for me said he could modify the original board to accept different types of signal tubes.

So my question is about the 7199 tubes. Should it be a go or no go??? I don't mind paying $30 each for the 7199 but I'm more concerned about the sound quality. He said the board could be modded to accept 6922 signal tubes which are better than the 7199.

Thanks

Maurice

[dcarlson]

Don't know but... I'll be interested to hear which way you go. Stock/non stock.

Are you planing on getting it fixed soon?

[organ]

Yeah. If everything goes well, I should have her playing again in about a month and a half. Everything will be replaced with better parts except the transformers. He said if the circuit board is still good it will stay. He's also going to re-chrome the chassis. I'm thinking about getting increased filter capacitance as well.

If I do get the circuit board modded, the JAN Philips and Sovtek 7199's will be for sale.

Maurice

[Tour2ma]

Sorry, can't help you maurice... There are about as many opinions on tweaking 70's as there are 70's owners. I've chosen to stay stock, or as stock as possible.

[organ]

That's cool. A lot of people like to keep it stock to retain its value. I don't plan to sell this amp, EVER! I'll ask about the mods on audioasylum. If you guys are interested in the answers I can post them here.

Maurice

[dcarlson]

Sounds cool.

I put the new RCA's in mine last night. I didn't have time to give a good listen and I won't have a chance to do so until next week.

[organ]

Awesome. Did you have to increase the size of the holes on the two boards holding the RCA's? I had to do that with mine. Did you manage to get them further apart?

Maurice

[dcarlson]

It's sort of temporarily set up for now. I used the mono/stereo switch hole for one and drilled a larger hole into the plastic piece for the other. Not the best looking but it works. ;)

Next up is the power cord. I'm still debating on the IEC inlet. It would make things so much easier powercord wise. I'll probably do it next week.

[Tour2ma]

maurice,
Please post a link to your Asylum thread here, and we'll follow a long.

[organ]

No luck on AA. I'll try dynaco-doctor.com and post a link if there's any response.

Maurice

[Brianomatic]

organ

Congrats on your Dynaco ST-70 purchase. I have owned the solid state Dynaco 400 and 416 amps and the PAT 5 preamp since the late 70's. I have modded some and had others do mods over the years.

I always wanted to get my feet wet in tube equipment and your thread is making me want to jump-in. Tube equipment has a sound of its own versus SS just as vinyl versus CD's. I remember studying tube technology in college (feeling old now) with all the biasing requirements and such. As you will learn, the tube equipment require regular maintenance in regard to keep the tubes operating within their design bias along the load line of the tube's characteristic curve.

Anyway, you had mentioned the Audio Research mod and I seen this on Ebay. It may be of some interest to you.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=39783&item=3094340597&rd=1

Regards

Brian

[organ]

Hi Brian,
Thanks a lot for the link. I will call the guy doing the restoration and ask if he could perform the AR mod if I provide the booklet. If he will, I'm going to purchase it. Thanks.

"As you will learn, the tube equipment require regular maintenance in regard to keep the tubes operating within their design bias along the load line of the tube's characteristic curve."

I've learned quite a bit about tube equipments when it was working. Well, it wasn't perfect when I first got it last summer. I had to replace the quad cap and bias supply. The amp started to go down hill in January or Feb. Can't wait until she's all good again. You're right about the maintenance. It's more work than SS equipments but the reward the amp gives you is really something else.

Maurice

[organ]

I think I found the problem. I started to wiggle the coupling caps around and a few of them were loose. The solder had gotten soft over time. I removed all 6 and re-soldered. So far so good. 1hr and no red plates yet:). Oh she sounds soooooo sweet:). I still plan to get it restored in about a month.

Maurice

[dcarlson]

Congrats...

I've been agonizing over a tube pre or speakers. A much as I would love to get new speakers I think a pre would be the wiser choice.

[organ]

I sure hope it was the coupling caps. It's been on for many hours and still working fine. The Svet's/JAN/Mullard are really singing.

A tube pre made a very big differece to me. Probably as big as adding a tube amp. I think going with a tube pre first is a better shoice. Your tube magic will increase 100%. Why don't you try out the 'Foreplay'? $150 and can be completed in a single night or two. www.bottlehead.com

Maurice

[dcarlson]

Good luck with it. :)

I've read about the Foreplay. Are there any other decent kits out there?

[organ]

Don't know any ther kits but there are a lot of upgrades available for the foreplay on the bottlehead website. They say it's best to build it normally first and then add the upgrades.

Which pre amps are you looking at right now?

Maurice

*edit* I just checked tubestore and they have a new batch of 7199 tubes. No pics or brands mentioned. It just says "NOS assorted brands" for $29 each. Cheaper than the JAN/Philips. The JAN/Philips are still $30 at triodeelectronic

[dcarlson]

None in particular just yet. I've got more reading to do.

I've read countless good things about the ST-70 and the foreplay pops up every now and then.

[organ]

OK, I'm sure it was the coupling caps. It was on all day and night until 6:30am and no problem at all. I only turned it off when I went for my smoke breaks. I still can't believe how good this amp sounds. Soundstage is HUGE and so much power for the Klipsch. AAAAAAAH:D

Yeah, quite a bit of people use the foreplay with their ST-70.

If you decide to try new power tubes give the EH6CA7 fat bottle a try. Less bloom and sweetness than SED but more detail, air, extension and power. Seems to dig lower too.

Now I'm thinking about which caps to replace the stock with. I've been doing a lot of reading and a lot of people say the coupling caps make a difference. The oil-in-paper are more mellow, lush and less detailed. The most popular ones are the big orange caps.

Maurice