So apparently my '73 50w Marshall has 100w output and power transformers...(pics added)

[Dogs of Doom]

And still no pictures.
Are you all fools?

he posted a couple from the imstagram post...

www.instagram.com/p/B9Zzzw3H-Fy

I downloaded them & posted them here:

imgur page

video:

 

[joshjoshjosh]

 

[joshjoshjosh]

Just got back from the gig. Due to venue logistics, my bud played his amp tonight so I didn't get to hear it live, but I did get it back home. Please excuse the midnight garage lighting.

 

[joshjoshjosh]

one more

 

[playloud]

Looks like the mystery is solved!

The OT is an older replacement. I've seen that type on a few US-based amps and I think someone here might know who the manufacturer/distributor was?

The PT is a Dagnall T3556 (the "D.E." stands for "Dagnall Electronics"), which is indeed a 100W PT! You can see how the rectifier has been modified to accommodate the center tap. I'm not sure exactly when these transformers were used in the 100W amps, but it was definitely during the '70s, so this is an early replacement indeed. I wonder if it was a casualty of the bias feed being dependent on the standby switch

P.S. The "D" in the serial number indicates '72.

 

[joshjoshjosh]

Looks like the mystery is solved!

The OT is an older replacement. I've seen that type on a few US-based amps and I think someone here might know who the manufacturer/distributor was?

The PT is a Dagnall T3556 (the "D.E." stands for "Dagnall Electronics"), which is indeed a 100W PT! You can see how the rectifier has been modified to accommodate the center tap. I'm not sure exactly when these transformers were used in the 100W amps, but it was definitely during the '70s, so this is an early replacement indeed. I wonder if it was a casualty of the bias feed being dependent on the standby switch

P.S. The "D" in the serial number indicates '72.

Well I greatly appreciate the info. Now I'm curious what happened to this amp for it to get this work done? I'm very excited to fire it up. I just put together an old Ampeg V4 cabinet with Celestion G12H30's on bottom and Greenback's on top. I think they will pair nicely.

 

[Ned B]

I believe the replacement 50W transformer came from Unicord and was US made. Music Dealer Service in Chicago used these and they were an authorized service center.

 

[Ken Underwood]

Well if nothing else then on the chassis label it is signed by Rosemary, the best, by far, hand wire`r Marshall ever had, quality.

 

[Resident 217]

Could be the power transformer mod was done to facilitate the use of a Variac ?
Probably last longer and be safer I think. Here's one that's modded with a 100w power transformer.

Biasing Friedmans 50w Marshall


that 73 looks like a seems nice and easy to work on amp. I may see if I can pick something up similar.
Thanks for all the pics.

 

[Ned B]

I'm wondering if using the 100W PT was more about the increased ma over the 50W which leans to being a bit current starved.

 

[joshjoshjosh]

So much for thinking it was stock! It's all good. I'm not really worried about it. It sounds amazing. I fired it up with the wife and baby gone. Boy, I don't think I have ever heard it sound so angry! Reverend Sensei and Tele into a few boosts, Jan Ray, SD-1, Metropoulos Supa-Boost. SD-1 was my least favorite, still sounded good. Supa-Boost fulfilled out its life missions and made the Marshall sound more Marshall-y, the shocker was the Jan Ray wit my Tele. Super punchy! I love the Jan Ray and have played it with a lot of amps. As you can imagine, it sounds great with Fender style amps. I figured it would just be ok. Concerning single coils, it knocked it out of the park. Ran that into my Ampeg V4 with Greenbacks and G12H30's. I also played it stereo with my Naylor.

 

[Gene Ballzz]

I'm betting that with that PT, the overall sound is tighter and the bottom end less mushy and flubby than a typical, otherwise similar 50 watt amp.
Just Surmisin'
Gene

 

[joshjoshjosh]

I'm betting that with that PT, the overall sound is tighter and the bottom end less mushy and flubby than a typical, otherwise similar 50 watt amp.
Just Surmisin'
Gene

Yeah the tech gave the same guess. Maybe little better bottom end. Maybe.

 

[neikeel]

Good to see complete pics - at last
Looks typical 72 to me (which jives with the D suffix).
Glad it sounds good. The tech used modern parts which is ok. I don’t like the bodge of radial bias caps - would bug me lots.
The original PT would be a Drake 1202-164. This era (voltages varied over the years) would be heaters 3.15-0-3.15 and HT 345-0-345. This would give operating HT of around 420vdc with the half wave rectifier block you see there with bias being derived from one of the ac HT feeds.
The 100w OT would have same heaters but 190-0-190 on the HT and dedicated 0-95v bias winding.
You can use that rectifier as full bridge by using all 4 internal diodes (ground the unused lug from the 50). I don’t see why the piggybacked diodes on the block unless it was faulty or they wanted more current handling capacity - but then diodes across all 4 surely?) Typically you would hook the HT CT to between the screen filter caps on a 100w.
Can’t tell what bias feed is derived from - given only 10k pre diode dropper likely the 95v dedicated feed.
I’d expect HT to be 480v or so which it could be a fire breather!

 

[Spanngitter]

Seen that once, on a '69 JMP50 , 100W PT shoving nearly 500Vdc onto the Anodes...First I was baffled about the voltage but then noticed that there was a way bigger PT installed then normal. So maybe there was a time where there was no 50W PT available or techs did think that the 100W PT can survive the Standby flaw better?
I need to see if I still have pics of that repair as I think I recall that all the solder joints had been original....

 

[mickeydg5]

And still no pictures.
Are you all fools?

Stop liking my post!

We are all fools on this ship.