Scratch building a RCA SP20, help with transformer and OPT needs.
- Thread starter Ken Boyd
- Start date
Plus, the Dynaco tranformers would be "reusable" if you decide you don't like the RCA design for some reason. You could move feedback to the transformer secondary, use a quad of EL84 (or the Russian equivalent), try a pair of EL34, experiment with UL, etc., etc. The sky's the limit! 
Jack
Jack
Checked the Dynakit site guess they are out of OPT transformers. Is there a source for them or do I just pick up what I can off the auction sites?
Seems strange as I found a few for sale used ones and they are coming from Japan, I would have thought those things would be pretty common in the states.
Seems strange as I found a few for sale used ones and they are coming from Japan, I would have thought those things would be pretty common in the states.
These Conn organ amps have quite good outputs and they are 4k+ impedance. These aren't too expensive either if you just need the transformers. You would have some other parts that might sell to compensate. Search Conn organ amp on ebay. There is also some good info about them here on AK. This is an interesting thread about them. Post #14 has a factory data sheet about them and lists them as 4k primary and 40W.
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Thermionic Lab in Greece makes what are reputed to be fine transformers. He has a Dynaco ST-70 compatible output for a resonable price. And he eats the tariff costs according to his home page.
www.thermioniclab.com
Dynaco ST70 Output Transformers Upgrade (Pair) VEB
Dynaco ST70 Output Transformer Upgrade (Pair). The transformers are suitable for upgrading dynaco ST70 amplifier or build a project based on ST70 topology. Please note that the transformers are not a drop through replacement. The transformers are built in a bigger core area with more...
www.thermioniclab.com
Doesn't @buglegirl's new venture have transformers in stock?
What is it named so we can look it up?
Has anyone tried the Dynaco A-470/clone output transformers MPS makes? Their ST35 transformer (z565) is quite good and relatively inexpensive.
I have a set of Matt's (MPS) transformers on my 6L6 amp and they seem to work pretty well. If he doesen't have anything listed maybe send an email to see if he has or can make you something. Mine were a semi-custom job using an existing lamination stack and bobbin to fit the dimensions I needed but wound to 6.6K instead of whatever his usual impedance options in that size were. Price was basically what he charges for catalog transformers, no special design or setup fees, and I got them pretty quick so I really have no complaints.
I have changed my plans to build them on a chassis, since I am so green at this I don't want to ruin a perfectly good chassis. So as of now my plan will be to build one on a sheet of aluminum with legs and use that as a test bed. When or if I get a unit working that I like, I will then use that to install on my chassis.
I do have a number of Luxman and OPT's and a pair coming that I think will work. I will post pics when the pair I have coming shows up. By building on a dummy platform I can make changes along the way until I have something that will work.
plan will be to build one on a sheet of aluminum with legs and use that as a test bed. When or if I get a unit working that I like, I will then use that to install on my chassis.I do have a number of Luxman and OPT's and a pair coming that I think will work. I will post pics when the pair I have coming shows up. By building on a dummy platform I can make changes along the way until I have something that will work.
if you do the sheet thing right you can just lose the legs and build a wood box around it with a recess matching the plate thickness routed around the inside edge. Drop the plate in, screw it down, done. Maybe do corner braces in the box so you have something to run retaining screws into.
Erhard kept the transformer business and I highly recommend his line of Lundahl transformers.
Frannie
My first 211 SET prototype was built on a piece of 3/4" MDF. Everything was mounted on top with transformers upside-down and tube sockets on standoffs. The thick MDF allowed screwing down strips of wood that surrounded the transformers to keep them in place. Capacitor clamps and a few terminal strips handled the rest of it. It was very quick to build up and no need to cut any metal.I have changed my plans to build them on a chassis, since I am so green at this I don't want to ruin a perfectly good chassis. So as of now my
Jack
my "breadboad" is kinda similar, the octal one is relay sockets attached to a piece of aluminum purely because thats how I found it. The non-octal one is a piece of scrap plywood with 9 pin sockets on boards that have screw-down terminal strips. each socket is surrounded by terminal strips to attach things wherever I need to. Totally useless for any sort of permanent assembly but damn handy for testing things out.
I had already purchased a pair off their ebay site prior to your warning. It all worked out well though, they never sent them, just created a label. I waited for a while but it never showed them actually in transit, so I contacted them but to no responses. I filed a claim with eBay and paypal and they promptly refunded my money. After that Pacific Magnetics responded with sorry, will check in with their shipper, that was the last I heard.
I have a couple of what I think would be good candidates that I have, 5K PP OPT's I puchased them a while back from a Japanese seller. But I am keeping my options open, haven't deciede on if I want to use them or not.