What should I do with this Output Transformer?

[skipwave]

Speaking of gapped output transformers...

I'm thinking the 6EM7 mike amp. Soon I will shut up about this thing and just build it, just haven't had any time.

This isn't exactly the impedance the 6EM7 wants, the Rp will be much lower than 9k. Probably meant for PP output, so used in a plate out design with center tap unconnected I expect less current handling than the rated 145ma.

Think it could handle B+ with the plate sitting at 50ma?

 

[skipwave]

Or........ a 417a/5842 mike amp following PRR's suggestions in this thread:

 

[CJ]

145 ma , lets say tubes mis matched by 10%, this gives 14.5 ma.

20ma, maybe. bass response will change as dc goes up.

 

[skipwave]

Tubes mismatched? You mean in PushPull config, right?

I'm interested in using this on a single plate, like in the 417 design that PRR suggested. Although, I know you are getting good results without an output tranny in your 417 pre. I just have to use this tranny somewhere. Otherwise, I'll get buyer's remorse. :wink:

 

[rafafredd]

Please, save this transformer for a PP vari mu 6V6 output. It´s perfect for the purpose. You can have a lookon many circuits, like Collins, Gates Stalevel, etc...

This is perfect for a pair of 6V6. You will have to folow it with a 600:600 attenuator, like in many many variable mu designs... It can be a bridge T or an unbalanced T. The unbalanced version works OK even if your line is balanced. I use an unbalanced T with mine and it´s ok.

With those 6V6 output sections, you can have a pretty fast control voltage, and use your vari mu with very fast attack. It sounds great.

You know, it´s not very easy to come across this type of trans. 30w, PP, 600z out??? mmmm ... Must be a Vari mu!

 

[skipwave]

[quote author="rafafredd"]Please, save this transformer for a PP vari mu 6V6 output. It´s perfect for the purpose. You can have a lookon many circuits, like Collins, Gates Stalevel, etc...[/quote]

Thanks Raf, I see what you mean. I just spent some time looking at the schemos from the Gates/Collins/Federal. Of the bunch, the Federal AM864 looks the most promising for a project, especially since others are currently working on it: Federal Limiter Thread

 

[rafafredd]

There´s a very simple Collins vari mu called the 356E. Have a look at this one. You can make changes to the sidechain, like I did to my STAlevel to make it variable attack and release, maybe even threshold...

 

[NewYorkDave]

Before all of yuz get too excited, are you sure it's not just a voice-grade job from a telephone amplifier or military radio? (Note the olive drab paint!). The freq. response spec is scratched off the case.

 

[rafafredd]

generally, when you use a higher power transformer in a lower power situation, you should get a better frequency response. Might be wrong, but I think you should try it. Even the old voice grade UTC transformers tend to work much better than what they spec.

 

[ciminosound]

I have to second the fact that sometimes "voice only" trannys perform better than spec (but not always!) I have an RCA that reads 300-4000Hz but performs in the 20-20,000 range as good as any UTC or Triad I have. On the other hand some voice only transformers suck.

 

[skipwave]

[quote author="NewYorkDave"]Before all of yuz get too excited, are you sure it's not just a voice-grade job from a telephone amplifier or military radio? (Note the olive drab paint!). The freq. response spec is scratched off the case.[/quote]

Yeah, isn't that convenient? I didn't notice when I bought it. :roll: The guy said he swept it 20-20k, but he didn't provide a plot or docs. I'll check the frequency response before I build anything specifically for it.

Edit: After much searching, found a picture of a model in the same series with complete markings: TF 1A 16 YY PRI 2500, 1000, 500, 250, 0, SEC 15 OHMS. Level 25 Watts Max. Fr. Resp. 50-15000 CY. +-2 dB. WV 50 W Peaks. Different application, but at least it means this series wasn't voice only. I looked through all the Stancor catalogs I could find and didn't see these, maybe they were made just for the military.

I can also vouch for the better-than-spec performance in certain transformers. I used an old Thordarson to build your re-amp and it works great.

 

[skipwave]

[quote author="rafafredd"]There´s a very simple Collins vari mu called the 356E. Have a look at this one. You can make changes to the sidechain, like I did to my STAlevel to make it variable attack and release, maybe even threshold...[/quote]

Thread with link to Collins 536E schemo.

That does look nice and simple. Hmmmmmmmmm.

6386 prices = Ouch!

People seem to think these are suitable substitutes: 5670. I'm going to have a closer look at the datasheets.

 

[rafafredd]

Use a pair of 6BA6´s... try many until you find a pair that works nice. Or you can match it with a good tube tester. I like to "match" in circuit.

 

[clintrubber]

[quote author="NewYorkDave"]Before all of yuz get too excited, are you sure it's not just a voice-grade job from a telephone amplifier or military radio? (Note the olive drab paint!). The freq. response spec is scratched off the case.[/quote]

That triggered me - I'm cleaning house and the time has come
to see what that green box has for usable parts.

Please have a look:
http://www.groupdiy.com/index.php?topic=13725

Thanks,

Peter

 

[skipwave]

[quote author="rafafredd"]Use a pair of 6BA6´s... try many until you find a pair that works nice. Or you can match it with a good tube tester. I like to "match" in circuit.[/quote]

Thanks for the tip, Raf! Those do look perfect to replace the dreaded 6386.

More about 6386 subs in this thread.