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EL84 se output transformer. These were out of a ECL82 reel tape amplifier. I measure about 5.5k ohms pins 1-4 with 8 ohms on 6-7. I plan on running 300v B+ with EL84. Should i use the tap for the screen as it was or use regular dropping resistor? I have read these are not real UL taps. 
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That doesn't seem right.Originally posted by mozz View Post"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz -
Impedance. Measured with a LCR meter as i always do. DC ohms is 200-300 which is about normal.Comment
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Need more info, like 'what do F and D represent'?.My band:- http://www.youtube.com/user/RedwingBandComment
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They are from the power supply. I am not using the original power transformer but i have 300v available.Comment
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Ah. Ok. That threw me off.Originally posted by mozz View Post"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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Questions are, should I use that tap on pin 5 , is it a UL tap, will it make any difference? Want to know before I mount the transformer. Long story short is it's a stereo tweed Princeton , 1 power supply, 2 turret boards, 2 x 8" speakers, 2 different output tubes, el84, 6gk6, one side is standard tweed Princeton other is Kalamazoo model 1. Yeah I like making things hard on myself.Comment
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To understand the circuit it is essential to see how "F" is wired .
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That sure seems a weird way of drawing an OT with a 'UL' tap (or whatever).
I'm another wondering if 'F' is an innie or an outie. Can you post the whole schematic?Originally posted by Enzo
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Appears F is derived from the voltage drop through the winding and the resistor?
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Ha - I've never seen this before... I'm going to speculate a bit. This appears to be a ripple suppression approach.Originally posted by mozz View Post
AC ripple at D causes currents to flow to the plate and the screen.
Those cancel in the transformer so ripple is suppressed.
At the same time, F is feeding the preamp tubes through the OT inductor (acting like a choke) and R57 with a filter cap C301, also reducing ripple.“If you have integrity, nothing else matters. If you don't have integrity, nothing else matters.”
-Alan K. Simpson, U.S. Senator, Wyoming, 1979-97
Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
https://sites.google.com/site/stringsandfrets/Comment
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UL works by feeding part of the plate signal to the screen.
As the screen connection seems to be decoupled from any signal by C301, it can't be UL.
A winding on a loaded transformer doesn't act like a choke.
But I like the idea with the ripple cancellation.
Depending on winding turns the 3.3k resistor would act as load and steal some output power, though.
So I'd expect a low turns count.
Still wondering if there's a schematic error with the OT wiring.
This said, I wouldn't go for UL with a guitar amp anyway.Last edited by Helmholtz; 05-21-2024, 10:55 PM.- Own Opinions Only -Comment
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There's also windings on pin 2 pin 3, joined together but i don't see them going anywhere.
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Here's another speculative idea:
As the 2 OT primary windings are antiphase wrt. point D, sending DC current through the lower part can reduce the net DC flux in the OT core, thus increasing saturation headroom.
Same thing naturally happens with PP operation.
This might make sense here, as this type of transformer core is unlikely to have an airgap, typically required with a SE OT to cope with the DC bias current.- Own Opinions Only -Comment
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