Bias tap from power transformer

[johnheath]

the heater winding in a big pwr xfmr could probably carry 20 amps or more, that is how big the wire is. primary wire is also usually way overkill, so no problems on that side either. the 7.5 amps spec is used so that you get 6.3 with a load of 7.5 amps, you can go up or down on the load and that 6.3 will move up and down just a tad.

Thank you sir

I do not believe that you are wrong about it ... the problem would be if it did not work out that way after you have bought a transformer for a lot of money?

I know that the transformers used in those 100W Marshalls are specified just enough to handle those values


Best regards

/John

 

[scott2000]

.......... every transformer I look at that will handle four EL34's doesn't have more current than 7,5A @ 6,3VAC. Using the four EL34 and two 6GH8 will draw near 7A... I guess that it would be on the limit of what such a transformer can handle... Am I wrong on this? It feels like I should have a bit more margin?

I know that the transformers used in those 100W Marshalls are specified just enough to handle those values
Best regards

/John

the heater winding in a big pwr xfmr could probably carry 20 amps or more, that is how big the wire is. primary wire is also usually way overkill, so no problems on that side either. the 7.5 amps spec is used so that you get 6.3 with a load of 7.5 amps, you can go up or down on the load and that 6.3 will move up and down just a tad.

Sounds like you are getting close???? I'm trying to follow along and would like to know this as well.....

 

[johnheath]

Sounds like you are getting close???? I'm trying to follow along and would like to know this as well.....

Yes, I am in fact getting close. Especially since I found out that Sowter has a couple of very interesting transformer for the job... please have a look at their 9157 and 9079... no bias tap but I guess I can copy something from the mentioned Ampeg and/ or Marshall?

Not to change the subject too much but do you guys have an opinion on the difference between Edcor output transformer like the CXPP50-6,6k and the Sowter UA21? I know that I don't post any data but they are similar with their bi-filar windings and impedance... the do have a major difference in prices though... 299USD for the Sowter and 75,55USD for the Edcor!

Best regards

/John

 

[abbey road d enfer]

Yes, I am in fact getting close. Especially since I found out that Sowter has a couple of very interesting transformer for the job... please have a look at their 9157 and 9079... no bias tap but I guess I can copy something from the mentioned Ampeg and/ or Marshall?

Not to change the subject too much but do you guys have an opinion on the difference between Edcor output transformer like the CXPP50-6,6k and the Sowter UA21? I know that I don't post any data but they are similar with their bi-filar windings and impedance... the do have a major difference in prices though... 299USD for the Sowter and 75,55USD for the Edcor!

Best regards

/John

I don't know specifically these two references, but I know that Sowter is a dedicated audio transformers mfgr, when Edcor is power transformer winder gone audio. To my knowledge Edcor use only M6 lams, when Sowter use whatever it takes to do the job optimally, Nickel, Supermalloy,... and they know exactly how electronics react with xfmrs, so they know everything about sandwiching, minimizing leakage and parasitics.
Now it depends on the degree of performance you're expecting. With a little trial and error a PT winder can make decent guitar amp OT's, but for something that would really qualify as HiFi, I would not take the risk of being disappointed.
Remember that leakage inductance and parasitic capacitance are serious issues when the amp is under significant NFB, which is bound to be the case for HiFi, not so much for guitar.

 

[johnheath]

I don't know specifically these two references, but I know that Sowter is a dedicated audio transformers mfgr, when Edcor is power transformer winder gone audio. To my knowledge Edcor use only M6 lams, when Sowter use whatever it takes to do the job optimally, Nickel, Supermalloy,... and they know exactly how electronics react with xfmrs, so they know everything about sandwiching, minimizing leakage and parasitics.
Now it depends on the degree of performance you're expecting. With a little trial and error a PT winder can make decent guitar amp OT's, but for something that would really qualify as HiFi, I would not take the risk of being disappointed.
Remember that leakage inductance and parasitic capacitance are serious issues when the amp is under significant NFB, which is bound to be the case for HiFi, not so much for guitar.

Yes I hear you. I frequently use Sowter input and output transformers when building mic press and comps and I have never had any issues with them. As mentioned before in this thread about having some issues with a Hammond PT... that problem was solved by getting a Sowter PT for that LA2A build and no vibrations from that one.

And I agree about the risk of disappointment so I have already started doing some calculations on using Sowters for both PT and OT's.


Thanks for your inputs

Best regards

/John

 

[PRR]

> Edcor is power transformer winder gone audio

EDCOR started, a long time ago, with wireless microphones. In and out of TeleType support(!). Commercial audio amplifiers and automatic mixers. Deaf aids. Got into wireless guitar, digital amps, multiplex snakes, but were too far ahead of the game. Absorbed Delta transformers (ex-Peerless folks). They dropped all else when major customers needed BIG crates of audio line transformers (small and speaker).

Yes, the do seem to be a "M6 shop" and list about as many power lumps as audio lumps. Not geeks like Sowter. But this is a *guitar* amp?? You don't need cyto-ferrite to make 2mA of 50V DC.

 

[buildafriend]

> Edcor is power transformer winder gone audio

EDCOR started, a long time ago, with wireless microphones. In and out of TeleType support(!). Commercial audio amplifiers and automatic mixers. Deaf aids. Got into wireless guitar, digital amps, multiplex snakes, but were too far ahead of the game. Absorbed Delta transformers (ex-Peerless folks). They dropped all else when major customers needed BIG crates of audio line transformers (small and speaker).

Yes, the do seem to be a "M6 shop" and list about as many power lumps as audio lumps. Not geeks like Sowter. But this is a *guitar* amp?? You don't need cyto-ferrite to make 2mA of 50V DC.

Interesting that some of the peerless people ended up there.. They do seem to be geeking at least a tiny bit still..

Mercury Magnetics does custom jobs too.. I've inquired. They want more money though.  It's just the turn around time that makes it tough.

I wish there was a better source for one off EI transformers. I would imagine it could nearly be automated by a machine

 

[CJ]

Antique  90 bones plus ship


https://www.tubesandmore.com/products/transformer-marshall-replacement-power-100-w

evilbay  65 bones  no bids

https://www.ebay.com/itm/NEW-Marshall-100-watt-power-transformer/263648653965?hash=item3d62af328d:g:z24AAOSwWwVa52oW

 

[johnheath]

> Edcor is power transformer winder gone audio

EDCOR started, a long time ago, with wireless microphones. In and out of TeleType support(!). Commercial audio amplifiers and automatic mixers. Deaf aids. Got into wireless guitar, digital amps, multiplex snakes, but were too far ahead of the game. Absorbed Delta transformers (ex-Peerless folks). They dropped all else when major customers needed BIG crates of audio line transformers (small and speaker).

Yes, the do seem to be a "M6 shop" and list about as many power lumps as audio lumps. Not geeks like Sowter. But this is a *guitar* amp?? You don't need cyto-ferrite to make 2mA of 50V DC.

Thank you sir for interesting facts.

I am sorry to say that I do not know what you mean with "cyto-ferrite"... anyway the transformer from Sowter do in fact have a 50V tap so there will be no worries in using that.

It is not meant to be a guitar amp... I am looking at the Dynaco ST70 as a reference for my build.

So why does the "Geeks" not like Sowter?

Best regards

/John

 

[johnheath]

Antique  90 bones plus ship


https://www.tubesandmore.com/products/transformer-marshall-replacement-power-100-w

evilbay  65 bones  no bids

https://www.ebay.com/itm/NEW-Marshall-100-watt-power-transformer/263648653965?hash=item3d62af328d:g:z24AAOSwWwVa52oW

Thank you sir

I have just laid my eyes on a Sowter power transformer with two 6,3VAC @ 4A secondaries and 350VAC C.T so for my build it will do.

Best regards

/John

 

[johnheath]

> Edcor is power transformer winder gone audio

EDCOR started, a long time ago, with wireless microphones. In and out of TeleType support(!). Commercial audio amplifiers and automatic mixers. Deaf aids. Got into wireless guitar, digital amps, multiplex snakes, but were too far ahead of the game. Absorbed Delta transformers (ex-Peerless folks). They dropped all else when major customers needed BIG crates of audio line transformers (small and speaker).

Yes, the do seem to be a "M6 shop" and list about as many power lumps as audio lumps. Not geeks like Sowter. But this is a *guitar* amp?? You don't need cyto-ferrite to make 2mA of 50V DC.

Hehe - had a second look at the Geek thing and I understands it now

Best regards

/John

 

[abbey road d enfer]

So why does the "Geeks" not like Sowter?

Language issue there. PRR's words "Not geks like Sowter", referring to Edcor. That means Edcor a not geeks, when Sowter are "geeks", meaning they are more savvy of the arcanes of audio than Edcor.

 

[johnheath]

Yes. I realized that a few minutes after I answered his post... Actually I learn a lot of english from just being, somewhat, active on this forum... so basically two sources of knowledge


Best regards

/John

 

[Bill Wilson]

Buy a new power transformer for Dynaco ST 70 amplifier, Triode Electronics makes one as does Hammond Industries..
I also found a power transformer w same specs at Allied Electronics, a few years ago.