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-   -   Old amp-rebuild or dismantle? (http://www.diyaudio.com/forums/tubes-valves/3987-old-amp-rebuild-dismantle.html)

taylor 11th June 2002 04:55 AM

Old amp-rebuild or dismantle?
 
2 Attachment(s)
Hi tube folk,
Got a question relating to a Soundcraftsmen interated amp I aquired. It was built about 1964 and is in good condition. I was going to upgrade the components in it but after listening to it for a week I am having second thoughts. It sounds muddy and lacking dynamics. My Pioneer garage receiver is far superior in sound. What should I do with it? Is it collectable or just another mediocre product. I am concerned that rebuilding it with be costly an may not successful. My other option is to dismantle it and build a simple amp using the trans, tubes etc. The thing is very complex having a dual mono pre ("transistorized") with a presence compensator, a center channel output, ambience control and electronic crossover etc. Not a simple amp like the ST70/PAS3 I once owned. It uses the following: EL86s, GZ34 rectifier, G.E.7247s, ATC 204/336 transformers and a cool blue neon looking tube for channel balancing. I hate to tear it apart but if its not marketable and sounds like crap, what can/should I do? Any direction or suggestions would greatly welcomed.

Taylor

planet10 11th June 2002 06:45 AM

Re: Old amp-rebuild or dismantle?
 
EL86s are kinda unique... sounds like with the complexity of the thing, it would do with a rebuild. Is it point-to-point wired... as a starter you could just wire a set of input jacks directly to the amps driver stage & use it that way as a 15W power amp.

If that is promising, you could start swapping out parts. The old carbon Rs usually have shifted in value and the bigger caps at least are usually in need of turfing.

With modern parts, some care with the phase splitter (maybe in a transformer) and a great deal of simplification i bet you could end up with something quite good -- certainly miles ahead of what it is today.

dave

taylor 12th June 2002 05:02 AM

Amp conversion
 
dave, thanks for the input. Bypassing the preamp is a good idea and will be my next move. Im hoping that the lack of performance is related to the pre. I can tell you that after opening the chassis up, I found a unbelievable amount of wiring (point/point). Theres got to be 100+ resistors alone and tracing all the wiring, well.... Anyway, if the amp sounds better, I'll start upgrading, but if not, I would like to use the parts and use a different design. You or anyone else know of a good amp design using the EL86s? I can remove the front panel and replace it w/ a new one and use the existing chassis w/ new wiring and parts.

Thx Taylor

planet10 12th June 2002 05:29 AM

Re: Amp conversion
 
Quote:

Originally posted by taylor
I can tell you that after opening the chassis up, I found a unbelievable amount of wiring (point/point). Theres got to be 100+ resistors alone and tracing all the wiring, well.... Anyway, if the amp sounds better, I'll start upgrading, but if not, I would like to use the parts and use a different design. You or anyone else know of a good amp design using the EL86s?
Tracing all that circuitry is a good excercise. Start with a blank piece of paper with the pin-outs of all the tubes on it. A good place to start with that data isDuncan Amps. You probably only need concern yourself with what comes after the volume control.

Info on the EL86 is scarcer than more common tubes -- the VTV FAQ says the SV83 is similar.

dave

MRehorst 13th June 2002 07:19 PM

If you decide to rip it up, you can use the output transformers to make some electrostatic speakers.

Sell the tubes on ebay for 3x what they are worth, and keep the knobs for future projects (or sell them on ebay, too).

Of course, you could just sell the whole thing (working condition!) on ebay. You'll get the absolutely highest possible price for it there. Use the money from the sale to get something more to your liking (or the parts to build it).

MR

Thatch_Ear 13th June 2002 10:48 PM

If you don't like the sound sell it. Keep it original and sell it on Ebay. Soundcraftsmens sell for good money and it looks to be in great cosmetic condition. The money could be used to build a kit or to buy something you know you like better. I am guilty of tearing old stuff apart but it is already trashed. I feel like vintage gear that looks as good as that one does deserves to be kept by somebody. Adopt it out for a good price and get a cosmetically challenged piece of Fisher for parts.
Thatch

planet10 13th June 2002 11:01 PM

Quote:

Originally posted by Thatch_Ear
get a cosmetically challenged piece of Fisher for parts.
or a Scott, or Pilot, some Lafayettes to name a few alternates

dave

FlMike 14th June 2002 12:05 AM

and if you do decide to sell it please let me know.




mike

taylor 14th June 2002 07:41 AM

After checking out the lack of EL86 design and feeling guilty about destroying a functioning unit, I suppose starting fresh is a better option. Ive never messed with Ebay but maybe Ill give it a try. I also have a matching tuner that seems to works fairly well also. So what would be a good entry level amp to build? I checked out the Darling amps and they look nice but only 1 watt isnt much. Ill be powering La Scalas and Fostex speakers so SE/low wattage is OK. I do want a quality sounding amp and not just an entry level project that will soon be unsatisfactory sonically.

Taylor

Thatch_Ear 14th June 2002 03:31 PM

2 Attachment(s)
The Mullard 3 is a good circuit and you can get the transformers for a pair of mono blocks from Chimera Labs for $400. I auditioned a pair of sample amps for a good 3 months and these were built by the tranformer winder and he used some really cheap parts and they blew me away. It was my 1st time with SE in my system and the soudstaging was a real treat and even with the 3 watts of the 6BQ5s it was plenty for my 92 db speaks. I recommend a few tweaks on the 50 year old design and with the high gain driver you don't need a preamp unless you need a phono section. Just a gain pot would work with CDs.


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