Sunn Model T Clone "75 Watts"

[DoomGuy666]

Hello fellow tube heads,

I have a question regarding my up coming amp build! I have built some kits in the past and have a good grasp on electronics and  tube amps!

The amp in question is a 1st gen Sunn model T.

PT:
Power: 200 W
Sec. 1: 375-0-375 V @ 201 mA
Sec. 2: 5 V CT @ 3 A
Sec. 3: 6,3 V CT @ 6 A

The PT should give me about 525 V DC. (375V AC x 1,4 = 525 V DC) is this right? Is this the voltage that ends up on the Plates??

Are 200 mA enough? As I understand it, I would technically bias the amp to around -50 to -55V. With the plate voltages at around 500V DC, the tubes (2xKT88 in Ultra Linear) would deliver around 50 Watts. So this should be enough, right?

OT:
Hammond 1650TA - Easy Wire
Audio: 120 W
Pri.: 1900 CT
Max. DC per Side: 403 mA
Sec.: 4-8-16 Ohm

Is this primary impedance good? Does someone know what primary impedance the original model T has?

And one last thing.. the choke..

The original model T has 2 chokes in parallel. Does this up the maximum voltage? In my opinion, with around 500V DC B+ I would technically need a 600V Choke.

Planning on using this one:

Hammond Choke 193N
Inductance: 3 H
DC Current: 500 mA
Resistance: 35 Ohm
Max. DC: 600 V

Or could I just use 2x 400V Chokes instead of the one 600V Choke? These 600V Chokes sadly are huge.
I just can't find any info about that..

That's all for now.. I hope someone can help me!

Greetings from Germany,
Matze

[uki]

Welcome to the forum!

This looks like a very interesting project! Which schematic are you following?
Could you post it? We like pictures too !! 

[pdf64]

550-600V HT with a 5k UL OT is the usual recipe for a pair of KT88.
Paralleling like chokes should increase the effective inductance and current capability, not the voltage. Voltage capability isn’t likely to be a problem.

[Latole]

Nice amp
Schematic ; https://el34world.com/charts/Schematics/files/Sunn/Sunn_model_t.pdf

Model T Super ; https://el34world.com/charts/Schematics/files/Sunn/Sunn_model_t_super.pdf

[PRR]

> 1st gen Sunn model T.
> 375-0-375 V @ 201 mA
> Are 200 mA enough?
> (2xKT88 in Ultra Linear)

Do research. As Latole's docs show, the Sunns were stuffed with 6550, and four of them. (Yes, KT88 is very near the same thing.) Now find Frank's and pull the G.E. 6550 datasheet (has UL data). Only one of the suggested conditions is 4k/pair (2k/quad), and that makes 70W/pair (140W/quad) and sucks 265mA+38mA per pair at full roar (606mA/quad, plus preamp 616mA).

201mA seems very shy of what you need.

If you propose a half-size two bottle at 70W, then your OT must be a lot closer to 4k than 1.9k. And you still need 300mA of B+.

The Sunn iron was semi-custom in 1973. It won't be generic iron. You can buy "Sunn replacement" transformers from the usual boutique winders. The prices are shocking. At least find out how much they weight; you can't do this job with less.

EDIT: image

[DoomGuy666]

Ok, thanks guys! This helped a lot!

The prices for custom model T PT's are totally ridiculous and overpriced. Especially for me living in the EU. Custom fees would probably just kill my project...

But I found a good alternative..

Hammond 378CX
Power: 465 W
Sec. 1: 400-0-400 V @ 534 mA
Sec. 2: 6,3 V CT @ 6 A

I also found this one: (probably to small Secondary Voltage....)

Hammond 373HX
Power: 369 W
Sec. 1: 350-0-350 V @ 403 mA
Sec. 2: 5 V C.T. @ 6 A
Sec. 3: 6.3 V C.T. @ 9 A

I also found a better suiting OT. With an impedance of around 5k and UL taps. Should be fine I guess.

[thetragichero]

i'm all for building clones of expensive or hard-to-find amps but philosophically i dig the spirit of the musicians i'm guessing you're into (based on username \m/) that involved using gear available for dirt cheap secondhand that nobody wanted (not only sunn stuff but old peavey amps for bands from new orleans... jazzmasters/jaguars/silvertone amps/etc from musicians of other styles). if you're in the eu you might could find an old loud hiwatt/sound city that could suit your needs. i'm not exactly complaining because you can sell darn near anything with a sunn badge (such as the pair of pa tweeters i found for nothing)

don't get me wrong some of those old sunn amps are damn fine pieces of kit (sceptre i had had more low end 'girth' than even the 200s bass amp) but anything based off of dynaco hi fi iron is gonna be pricey

[DoomGuy666]

Not really. I mean, sure there is some mystique surrounding the model T, but I'm not building it because of the whole hype.

I had an JTM45 clone. Sounded fantastic. But it was a bit low on volume. Sure it was loud enough, but it didn't have loud cleans. So I modded it to having a SS-Rectifier and while I was in there, I asked myself how a model T preamp would sound in this thing. So I modded the whole preamp, presence control and the phase inverter and viola! It sounds amazing. But now I still need more volume and for this I'll have to build a completly new UL amp. And after that I'll mod the JTM to standard spec. That's the whole story :D

BTW:

I found an even better suiting PT.
A Soldano Powert Transformer. Custom wound.

Primär: 120, 230 & 240 V @ 50 Hz
Sec. 1: 720 V C.T. @ 400 mA, 60 V Bias Tap
Sec. 2: 6,3 V C.T. @ 7,5 A
Sec. 3: 6,3 V C.T. @ 3 A

I will post pictures and so on when I start working on the project. At the moment I'm just planning. Schematic coming soon!

[DoomGuy666]

All in all. This project will cost me around 550 Euros. :)

[owen]

very excited to see how you get on. I was raised on Sunn and Ampegs when I started playing (very late 90s) instead of fender and marshall and have been missing my Sunn amps a ton lately.