non UL iron

a 3W single ended EL84 amp for home, work & school

non UL iron

Postby justinsweber » Mon Jun 24, 2013 2:09 am

I was hoping to use some trnascendar Iron I had... can anyone share... does the output iron need to be Ultra Linear? I have great transcendar 5watt iron... just not UL. Otherwise time to call edcor.

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Re: non UL iron

Postby Geek » Mon Jun 24, 2013 3:48 am

You can "fake" UL with a few external parts ;)

See the schematic here: ... pic=4706.0
(there's been updates since)

-= Gregg =-
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Re: non UL iron

Postby EWBrown » Thu Jul 11, 2013 7:45 pm

The "old school" method to implement pentode mode of operation, would be to connect the 6BQ5's screen grid to the B+ side of the OPT,
use a "stopper" resistor, 470 to 1K ohm, 1W.

Connect each of the screen grids (J2-2 ; and J3-2 on the PC board), back to J6 (+288V for outputs), using 470 ohm to 1K, 1W resistors as the "jumpers".


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Re: non UL iron

Postby Shannon Parks » Sat Jul 13, 2013 5:09 am

Or you can just do triode mode with 100 ohm resistors. I think it'll be around 1.5W instead of 3W.

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Re: non UL iron

Postby wildmouse » Mon Dec 14, 2015 2:19 am

Hi all
Im building a Budgie SE, Using Hammond Iron , 369jx and 125cse opt .
as there is no centre tap, should I incorperate a triode , pentode switch.
using 100 ohm resistor switched from screen grid to plate, and for triode mode a 1k ohm switched from screen grid to b+
I like the idea of a switch to try the different modes ,could UL be faked somehow
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Re: non UL iron

Postby GrahamJ » Mon Dec 14, 2015 4:35 am

Hi Wildmouse,
I wish you better luck than I had with the Hammond 369JX.
Unfortunately, with my Budgie SE that particular transformer wasn't up to the job.
I have ended up purchasing a second transformer, the Hammond 370DAX.
As expected, I now have some over voltage issues but I am getting there thanks to the fact that I only have the tough 6P14P Russian output valves.
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Re: non UL iron

Postby wildmouse » Tue Dec 15, 2015 1:56 am

Thanks GrahamJ
maybe mine will draw less power in triode mode, otherwise i will have to wait until i next go to singapore to buy a bigger transformer
I would love the edcors , but no suppliers in australia that i can find
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Re: non UL iron

Postby wildmouse » Fri Jan 01, 2016 5:40 am

hi all
finally got the amp up and running
no noise, no hum
bass a bit weak not helped by the hammond 125cse opt trannnys
otherwise the sound is great
the 369jx power tranny runs hot, can touch it for 2 sec only
cause i have no centretap on the tx i have run it in pentode and triode mode switchable
triode mode sounds better and easily loud enough
2watts, at half volume im worried about my zigmahornet speakers
even my wharfdale e 20s sound loud and clear
I used aerial coax for my input shield grounded at input, and another star ground at the power socket
as u can see my wiring is messy ,but this is my 1st attempt at point to point wiring
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