| Author |
Topic: Wiring a multi tap OT in a blackface Super Reverb |
Pete McAvity
From:
St. Louis, Missouri USA
|
Posted 9 Oct 2021 9:08 am |
|
Good afternoon, Electronics section. I’m hoping a fellow forumite can give a recommendation on how (and opinions on the best configuration) to wire a replacement output transformer for a blackface SR. I have a ‘65 dumpster save that is functional after cap swap & 3 prong power cord placed. I’m pulling the original 2Ohm, 40W OT & placing a Hammond 1760L 4/8/16 ohm switchable in its place in order to properly drive either one or two cabs loaded w/ 8Ohm JBL K130s. Anyone have, or know where to locate a wiring diagram? Thoughts on wiring with the primary & EXT jacks as they are vs adding an impedance selector switch?
Thanks,
Pete
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!"
Last edited by Pete McAvity on 9 Oct 2021 12:34 pm; edited 1 time in total |
|
|
 |
Bill A. Moore
From:
Silver City, New Mexico, USA
|
Posted 9 Oct 2021 9:56 am
|
|
| I wired my DR like the Hot Rod series with a switching jack. Main jack only is 8 ohms, when another plug is inserted into the Aux jack, the jack switches to the 4 ohm tap! |
|
|
|
Pete McAvity
From:
St. Louis, Missouri USA
|
Posted 9 Oct 2021 11:11 am
|
|
Now we’re talking. Now- what goes where? I can decide what resistance each wire is associated with from specs supplied in Hammond’s site- I just don’t know what to solder to what, or how to attach the four wires on the other end. I refer to do something like this that has 8 as primary & defaults to 4 when a second cab is plugged in- no dire need for a 16 ohm option. If I ever find myself using one 16 ohm speaker, I’ll tolerate the mismatch.
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!" |
|
|
|
Jeff Highland
From:
New South Wales, Australia
|
Posted 9 Oct 2021 12:57 pm
|
|
Wire colours are on the label, https://nextgenguitars.ca/products/hammond-1760j-output-transformer-upgrade-4-8-16-ohm.html
Common goes to the sleeve on the jacks the 4 ohm or 8 ohm goes to the tip.
Best not to use the term "primary" for the outputs, this is used for the other side of the transformer.
Rather than use a switching jack set up you could just wire up one jack at 8 the other at 4 and daisy chain the two speakers from the 4 ohm.Possibly more reliable than the switching jack.
_________________
Duesenberg Fairytale
1949 Supro Supreme
1950 National New Yorker
2008 Highland Baritone Weissenborn
2020 Highland New Yorker.
2020 Highland Mohan Veena
2021 Highland Weissencone |
|
|
|
Bill A. Moore
From:
Silver City, New Mexico, USA
|
Posted 9 Oct 2021 4:38 pm
|
|
If you use a shorting jack for the Main, (like Fender does), you will keep your amp protected from an open circuit. By using a switching jack for the Aux, you leave the standard shorting jack, but switch impedance with another speaker plugged in. I always leave my cab speaker connected, but it is possible to connect a 4 ohm only load if you put a dummy plug in the Main, and plug the speaker into the Aux.
I'm posting at home on my tablet, when I get to the shop, I can send you a schematic. |
|
|
|
Pete McAvity
From:
St. Louis, Missouri USA
|
Posted 9 Oct 2021 5:26 pm
|
|
Fantastic! Thanks Bill. If you could send it to my forum linked email I’d greatly appreciate it.
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!" |
|
|
|
Ken Fox
From:
Nashville GA USA
|
Posted 10 Oct 2021 5:03 am Hammond transformers
|
|
Great transformers. I used one for a Twin Reverb many years ago. It squealed like a stuck pig. I finally found with the scope that I was getting positive feedback to the inverter stage. Should be negative feedback. Solution was to reverse the transformers primary wiring to the power tubes. That changed the phase and corrected the issue
The colors of the primary wires were in fact the same as the original Fender transformer but still phased backwards |
|
|
|
Ken Fox
From:
Nashville GA USA
|
Posted 10 Oct 2021 5:13 am Fender Twin
|
|
On the 135 watt Twin Reverb amps a switching jack was used to allow properly matching speaker load to the output transformer
 |
|
|
|
Ken Fox
From:
Nashville GA USA
|
|
|
|
Bill A. Moore
From:
Silver City, New Mexico, USA
|
Posted 10 Oct 2021 5:23 am
|
|
| Switchcraft 13a is the correct switching jack. |
|
|
|
Pete McAvity
From:
St. Louis, Missouri USA
|
Posted 10 Oct 2021 6:30 am
|
|
Thanks guys! Ken- you were my next stop. I did a search here before posting & took note of the Showman combo you made. I’ve admired your handiwork here for years. Bill- thank you again- gonna order that switchcraft jack now.
Is the original first (no more of this “primary†confusion on my part) output considered a shorting jack that I can use w/ the new switchcraft in the EXT position, or do I need to swap it too?
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!" |
|
|
|
Ken Fox
From:
Nashville GA USA
|
Posted 10 Oct 2021 8:07 am Jack
|
|
| I’m sure the original jack would remain with the kit from Antique Electronics |
|
|
|
Bill Hatcher
From:
Atlanta Ga. USA
|
Posted 11 Oct 2021 4:35 am
|
|
ditto on what ken said about squealing noise upon firing up the amp. just reverse the leads. been there...done that.
do you still have the 2ohm original fender output tformer?
if so, just hook it into 4ohm loads and you will be fine. 8 or 16ohm loads not so good a match. |
|
|
|
Pete McAvity
From:
St. Louis, Missouri USA
|
Posted 11 Oct 2021 5:08 am
|
|
Thanks, Bill. Planning on running either one or two cabs w/ 8 Ohm K130s. If I leave the stock OT my only option is running both cabs. After the swap I’ll have the option of going down to one cab, which would displease the amp as it sits.
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!" |
|
|
|
Pete McAvity
From:
St. Louis, Missouri USA
|
Posted 28 Nov 2021 1:26 pm At the drawing board again
|
|
I carved out some time & got everything together. I went ahead with Ken’s suggestion & bought a rotary impedance selector w/ jack already wired. The P-H1600 selector is designed for the 1600 series Hammond OTs, and since the applicable 1600s & 1700s are multi-tap 4/8/16, I figured I could just look at the diagram for wiring a 1600 & make adjustments as needed to suit the 1760L that I’m using.
I can’t.
Looks like the 1600 series all have 5 secondary wires, each rated 0, 4 or 8 Ohms, and combinations therein result in 4/8/16 switching. The 1700 series have 4 secondaries: COM/4/8/16. Here’s the 1650N, which appears to be the closest equivalent to the 1760L:
https://www.hammfg.com/files/parts/pdf/1650N.pdf
And the 1760L I’m installing:
https://www.hammfg.com/files/parts/pdf/1760L.pdf
And hookup/data on the rotary switch:
https://www.tubesandmore.com/sites/default/files/associated_files/p-h1600_wiring.pdf
Based on this info- anyone see a way to wire the 1760L to this switch for 4/8/16 ohm options? And a bonus question: the selector actually allows for 4 positions. Can position four be configured as a “nothing happens†setting as opposed to “magic smoke†setting in the event that it accidentally gets flipped all the way over?
That’s a lot of info. I thank you all in advance for reading/doing my homework.
_________________
Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!" |
|
|
|
Bill A. Moore
From:
Silver City, New Mexico, USA
|
Posted 28 Nov 2021 3:05 pm
|
|
| I wouldn't bother with that switch, just use a standard 3 position switch. I installed a Marshall on my Twin clone, but there are cheaper one's from tubes and more. I used one of the Hammond 1600 series OT in my DR build, but I wasn't interested in having a 16 ohm tap. |
|
|
|
