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WTB 2.5K - 8ohm OPT

John,

I hope all is well. I'm guessing that you're looking for more budget type of transformers which I certainly can respect, oftentimes cheap is cheerful! There are two budget options for new transformers out there that come readily to mind.

One would be Edcor. I really like their transformers - both output and power. They make a 3K to 8 ohm 10 watt one here: EDCOR - XSE10-8-3K or you can spend a bit more and get one with end bells that is actually 2.5K to 8 ohms here: EDCOR - GXSE10-8-2.5K

Another really budget possibility would be the Speco T7010 transformers. They have multiple taps and just from memory, I thought they had one tap that would provide close to a 2.5K primary. They can be had for around $5.00 if you look around online. For fun I ran them up to 50ma at around 320volts before on a EL34 amp and they were beginning to show signs of saturation, but were fine below that. They start to have rolloff at around 100hz but aren't terribly thin sounding and have a respectable midrange sound...overall quite pleasant and much better than expected for pocket change ;>)

There's a guy on ebay with username Gobble75 in Phoenixville Pa (not sure how far that is from you), that used to have the T7010 transformers (probably still does but doesn't have them listed right now as far as I could tell). I've bought a variety of things from him over the years and he's a cool guy. He might be worth contacting as well to see if he has anything that would work (he always has a ton of surplus tube gear!)

Good luck finishing your amp project. Little single ended amps are a lot of fun!


Eric
 
John,

I hope all is well. I'm guessing that you're looking for more budget type of transformers which I certainly can respect, oftentimes cheap is cheerful! There are two budget options for new transformers out there that come readily to mind.

One would be Edcor. I really like their transformers - both output and power. They make a 3K to 8 ohm 10 watt one here: EDCOR - XSE10-8-3K or you can spend a bit more and get one with end bells that is actually 2.5K to 8 ohms here: EDCOR - GXSE10-8-2.5K

Another really budget possibility would be the Speco T7010 transformers. They have multiple taps and just from memory, I thought they had one tap that would provide close to a 2.5K primary. They can be had for around $5.00 if you look around online. For fun I ran them up to 50ma at around 320volts before on a EL34 amp and they were beginning to show signs of saturation, but were fine below that. They start to have rolloff at around 100hz but aren't terribly thin sounding and have a respectable midrange sound...overall quite pleasant and much better than expected for pocket change ;>)

There's a guy on ebay with username Gobble75 in Phoenixville Pa (not sure how far that is from you), that used to have the T7010 transformers (probably still does but doesn't have them listed right now as far as I could tell). I've bought a variety of things from him over the years and he's a cool guy. He might be worth contacting as well to see if he has anything that would work (he always has a ton of surplus tube gear!)

Good luck finishing your amp project. Little single ended amps are a lot of fun!


Eric
Hi Eric,,
Thanks for the info,,, I have the amp running, sounds really good, considering what I started with, I could pick up about a half watt output, with the right transformers... Phoenixville is about 15 miles from me, so not out of teh question,,,You know, timing is everything,,, while I was rebuilding this little amp,, I looked at the AES site for parts,, and noticed they had some of these little OPT's that I need, however, I just started, and didn't realize the original 4ohm OPTs would cut down the power output so much,,, when I went back to get them,, ($6 apiece!!!),, they were out of them, and said they wouldn't be getting any more...

I did look at teh Edcors,, they are way too big for this little chassis, not to mention out of budget...I believe the AA5 radios used the little OPTs that I could use,,, but I don't know where to get a pair of them,,, probably what AES had left over ....
I will check out the local guy you mentioned,,,
Thanks again for teh reply...
Regards,
John
 
John,

There's a guy on ebay with username Gobble75 in Phoenixville Pa (not sure how far that is from you), that used to have the T7010 transformers


I bought 4 from the gobble guy years ago...misplaced them, found them Friday for a project I want to continue with.

I looked up the Speco T-7010 on line, and there are alot of unhappy people now because the part has been redesigned keeping the same part number. The size is smaller, the taps are different, and some people on the Antique Radio Forum declared the new design nearly useless for tube amps now, at least push-pull ones. I think the inductance was also claimed to be far lower than the original. Unfortunately, they were designed for a different purpose, but found 'off-label' use in amplifiers.

Do a little research before buying the Speco T-7010 for tube amp OPT's. Luckily, mine are the older design.
 

knockbill

Member
2013-02-26 1:18 pm
SE PA
I know that guy,,, saw transformers at a Hamfest,, I believe them to be some kind of line (70V) matching transformers, that can work, some what on an amp,,, Not hifi, I don't think???
Anyway, I used the OPTs that were on amp, they have FB taps, and sound pretty good...

Now, I'm hunting for a single Motorola bass channel OPT, from a 3channel console amp... I have one, but its bad,,,
Any ideas?

Regards,
John
 

knockbill

Member
2013-02-26 1:18 pm
SE PA
A couple of years ago I started an amp using the 25C5's and this transformer. I never finished it before I got bored with it though.

10W Speaker Line Matching Transformer | TR7025-10W (TR702510W) | Distributed By MCM

Here is a thread you may find interesting:

Parsimon: An Ultra-Cheap DIY Class AB PP Pentode Power Amp - AudioKarma.org Home Audio Stereo Discussion Forums


Thanks for the links,,, I like to build small (>15W amps)... I have a lot of tubes to try, not many OPTs tho,,, and, I hate to buy new ones to try out an idea,,, I browsed the 25C5PP amp, looks interesting, I'll have to read it again...

Regards,
John