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Webster output transformers

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Posted on November 20, 2019 at 08:28:00
wclarson12
Audiophile

Posts: 21
Location: Hudson Valley NY
Joined: April 10, 2014
Hello all.
I just received a Webster 2A3 organ amp I purchased on Ebay.
The Webster outputs are gapped.
Has this already been determined?

 

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RE: Webster output transformers, posted on November 22, 2019 at 11:45:07
Stuben
Audiophile

Posts: 659
Location: Guber Ohio
Joined: December 30, 2005
Contributor
  Since:
May 22, 2009
Hey wclarson12,

If gapped, it's probably SE. So yes the max usable current on the primaries is fixed. The gap is to permit constant current (Class A) operation without saturation. Class A is the default characteristic of a Single Ended topology. Do you plan to re purpose the transformer?

Stuben

 

RE: Webster output transformers, posted on November 23, 2019 at 17:05:14
Alpha Al
Industry Professional

Posts: 2696
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since:
December 3, 2015
If it's the amp I think it is, it uses four 2A3's in PPP driving field-coil speakers.

About 10 years ago on this forum, there were multiple discussions of using these output transformers in SET amps, because they are air-gapped.

A search should find the threads, but I don't have the patience.

 

RE: Webster output transformers, posted on November 28, 2019 at 07:22:53
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
I wonder why a push pull output transformer would be gapped?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Webster output transformers, posted on November 29, 2019 at 05:31:11
dave slagle
Manufacturer

Posts: 5194
Location: NYC
Joined: April 27, 2001
chances are there will always be some DC offset. Adding a small gap helps account for this and allows a much wider range of "acceptable" operation at the cost of a bit of inductance.

dave

 

RE: Webster output transformers, posted on November 30, 2019 at 17:21:28
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
Yes, I understand a small gap to account for a little DC offset but enough to allow for SE use?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Webster output transformers ..Yes..., posted on December 1, 2019 at 19:08:12
drummerwill
Audiophile

Posts: 942
Location: St Louis Mo.
Joined: January 7, 2003

...I used them once in a parafeed 45 output SET amp with decent results... This was a junk-box type project.


Willie

 

RE: Webster output transformers, posted on December 2, 2019 at 06:56:15
dave slagle
Manufacturer

Posts: 5194
Location: NYC
Joined: April 27, 2001
the whole small gap thing is actually hugely misunderstood when it comes to EI lams. The only way to get a gap "suitable" for any DC offset is to have a completely discrete gap with all of the E's on one side and the I's on the other. I think much of the misinformation about alternately stacking the E's and I's in groups to decrease the size of the airgap comes from Rueben Lee





I find that this graph will work well for predicting AC permeability at a given excitation level but has no relation to DC saturation characteristics. In other words a 0.001" gap with EI lams alternately stacked in groups of 4 will behave very differently with respect to DC than a well polished C-core with the same effective gap.

I have mentioned this before in the John Hogan amp discussions and essentially adding a substantial DC offset to a PP output transformer actually linearizes the inductance as can be seen in the plot below of a ST-70 output.





given that the inductance you end up with is not huge, the listening reports seem to support that it can still sound really good and the math says response down to 40 hz shouldn't be a problem.

dave

 

RE: Webster output transformers, posted on December 2, 2019 at 09:29:18
tube wrangler
Manufacturer

Posts: 2217
Location: USA
Joined: January 29, 2007
Hi Dave!

This makes total sense to me.

People have run P/P transformers in SE
mode successfully (reports from others-- I
haven't tried it) when plate current is
held at about 1/3 of the transformer's rating--
or less.

My thinking on it is that different P/P
manufacturers build differently, so one
can only guess.

If anyone's going to do this, why not try
different current levels (on a given P/P
trans-- running SE) until you find an area where
you hear (or observe on your O'scope or analyzer)--
no saturation problems at full output-- and THEN,
take a good look at performance as you lower drive
levels.

Depending on what you find, you may elect to change
standing current level.

Full output isn't all that you need to know--
how does the trans behave at ANY chosen output level?

-Dennis-

 

RE: Webster output transformers, posted on December 3, 2019 at 08:02:34
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
I should try some of my many PP transformers in my SE amps.

I don't use my SE amps for bass to start with.

I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?

Thanks.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?", posted on December 3, 2019 at 08:41:33
Ivan303
Audiophile

Posts: 41384
Location: Cadiere d'azur FRANCE - Santa Fe, NM
Joined: February 26, 2001
Put that HK Cit II OPT BACK in the amp it belongs in THIS VERY MINUTE!

Jim will not be pleased if you don't. :-)



 

RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?", posted on December 3, 2019 at 09:10:15
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
Sorry. That amp is long gone and it wasn't of my doing.

These OPTs did sound nice in a PP 300b amps that I once had.
I may have to rebuild them. They had a little more power and punch than the SE 300b amps I have now but a little less "you are there".

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Webster output transformers, posted on December 3, 2019 at 09:54:10
dave slagle
Manufacturer

Posts: 5194
Location: NYC
Joined: April 27, 2001
Generally PP outputs do not perform very well SE because the ground reference that all of the capacitances are designed around is moved from the CT to another location. This can make the high frequency behavior unpredictable. Pushing a PP output to SE use with vintage "found" outputs like the Websters is one thing but pushing a top notch PP output into SE use is probably not the best thing to do. Of course you can give it a try and report back but ultimately that transformer is worth a lot more being used in the amp it was designed for.

dave

 

"you are there", posted on December 3, 2019 at 11:35:54
is a circuit issue not a SE or PP issue.

 

RE: "you are there", posted on December 3, 2019 at 12:13:17
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
Cool. Maybe you can school me about that.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: "you are there", posted on December 3, 2019 at 13:05:45
I already shared my efforts in this area months ago. If you were at all serious you would have tried it.
Unlike numerous cry babies on this forum, YOU actually have all the parts, the time, the expertise, and the ears/knowledge to discern an improvement or not. BUT, righteous prejudice (now taking the form of humoring) keeps you from discovering it.

 

RE: "you are there", posted on December 3, 2019 at 16:20:43
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
was it the 6GM5/WE133A ?

I found your posts but they come up blank.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: "you are there", posted on December 3, 2019 at 17:08:29
Are you just poking at me?

I really don't post on this forum to antagonize, I do anyway sometimes obviously, but that's truly not my premise. I've been through a fair amount in this hobby, I try to offer the top best of my findings, I really do.

 

RE: "you are there", posted on December 3, 2019 at 20:01:08
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
No, I'm not poking at you.

"I already shared my efforts in this area months ago"

I'm trying to figure out if the 6GM5/WE133A is what you are referring to.

when I looked up your posts about the 6GM5/WE133A many of them came up blank, no text.

No joke, no poking.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: "you are there", posted on December 4, 2019 at 12:06:40
Yes and no. I'm referring in a general sense to the basic topology of the WE133A which is PP pentode drivers with phase inverting input trans and the use of the two types of FB necessary. I think triode outputs could be fine here, with obvious adjustments necessary. This is why I keep asking about the math so I can try different combos, rather than just trial and error. Because I don't yet get all that, I think sticking to the known values is a good place to start.

You could make a WE133A 6GM5/7591 version which I would recommend, but there's numerous other choices.

There's the Langevin version 6SJ7/6V6, there's the McCurdy version 6AU6/6BQ5 (both from the pro sound world) and the consumer grade RCA RC-10 or RC-20. The later two use no cap in the FB circuit so they stand up the driver cathode on a big resistor. This forces the need for caps from the input trans (McCurdy) or tube PI (RCA) which I don't suggest. UTC even made a kit amp like this using 6AU6/5881 with a 12AX7 PI, but as Crowhurst would say and I agree, "if 2 stages can't get it done, then you need to start over."

If you have 4 good 7591's I'd say use them. Copy the 133A otherwise, but use a 450VDC rail. 10K OPT or close. The spec'd 600/50K split input will be too much gain for your system so use a lesser step up or be prepared to turn down a bunch. These circuits we designed to be driven from a pre-amp step Down OPT, hence the extra gain you don't need.
Put 400VDC on the screens through a dropping R and cap, and use a voltage divider for 275V for the front end. I used a pair of 400 ohm Rk for the outputs. I adjusted the FB resistor by ear to 267K. You may want to play with that value to see how this behaves. You should see about 18-19v at the cathodes, which is the same for 6F6. The test points in the 133A for the drivers is helpful, just roll tubes until you get a decent pair, same with the outputs. The series combo of the cap and R in parallel with the cathode circuit is the 18K throw away filter. Use it. It's because, as the RCA manual states, this type of FB brings a rise in the response at each end of the spectrum, which holds up the bass well, but must be an issue above 18K so "they" decided to chuck it. Makes sense. I truly hope you like what you hear. I got my grid "clips" from one of the old radio dealers, if you can't find any I can send you some. You can also make them from solid wire. You could use 6SJ7, but I didn't. 1620's are ideal here, but all they are is a selected low noise 6J7, and there's plenty of 6J7's that still qualify.

One last reminder also from Crowhurst, is that I believe he said something like, "FB used to make a bad design "better" is a sideways affair at best, while the sparing use of FB applied to a good design can make a good amp excellent"

 

RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?", posted on January 2, 2020 at 05:48:59
PakProtector
Audiophile

Posts: 11771
Joined: May 14, 2002
don't worry, the amps are already expensive enough to prevent most of the experimentation.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: "I wonder what a HK Cit2 OPT with 60ma. standing current on it would sound like?", posted on January 2, 2020 at 12:12:06
Tre'
Industry Professional

Posts: 14597
Location: So. Cal.
Joined: February 9, 2002
This pair of output transformers are long separated from the amp.

The amp is long gone. Not of my doing.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

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