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Old amp-rebuild or dismantle?

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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
 

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frugal-phile™
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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
 
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
 
frugal-phile™
Joined 2001
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Re: Amp conversion

taylor said:
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
 
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
 
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
 
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
 
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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Looks like a version of the Williamson circuit which has been around since the 40s. Getting a pair of PP outputs with an ultralinear can be fairly expensive as well. Good transformers will be the most expensive part of your amp/amps unless you get very lucky and find an old parts amp with what you need. $400 for 4 custom wound transformers for Single Ended mono blocks is really a good price. But if you want something as a complete kit that is not too expensive go to <http://gabevee.tripod.com>
I understand Gabe has been ill so I an not sure if he is still putting kits together but he had a kit for $450 that included tubes,chassis etc that is a SE 6L6 with 6SL7 drivers.
 
I second that motion. The whole lot is quite reasonably priced, plus you have the option of trying different o/put tubes in the same cirtcuit that are basically the same, ie; EL37, KT66, or the much neglected (because it's cheap & plentiful though nice sounding) 807...
tomcat
 
frugal-phile™
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Thatch_Ear said:
Lets hear about that 807 Tom.

An 807 thread.

There are a number of 807 equivalents: 1625, Raytheon RK-39 (IIRC), 5B254M (someone just gave me a bucket with a dozen of these). I also have some others but can't recall the numbers.

All have top caps which may be one of the reasons they are not given their due consideration.

dave
 
The 6L6 SE on Gabes site looks like a good value unfortunately he apprears to be out of business for the moment. Is this amps circuit the one thats able to use the different output tube types? If so, it would be an ideal experimental amp for someone like me who really doesnt know what all the various tubes sound like. Ive also been directed towards the Bottlehead Paramour. Any comments on this one. The price is right and they seem to have a big following. By the way, does anyone know the make of the transformers on my Soundcraftmen. Someone inquired and I cant find an actual name on them. They all have "ATC xxxxx" on them and a model number and thats it.

taylor
 
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