Sunn Model T

[CJ]

on the bench today is this thing>

 

[CJ]

dual pwr supply chokes in parallel,

 

[CJ]

like the copper plate input,

p to p right onto the tube sockets,

 

[CJ]

Solid State rect,

Mallory 20uf at 600 V,

those are usually two caps under the cardboard in series to get that kind of a rating back in 72 or even today.

 

[CJ]

looks like a couple of Tungsol 6550's went for a nap and never woke up,

bias probably ran away on that pair and they hogged all the current away from the other pair,

 

[CJ]

mint shape, no soldering iron has touched the chassis, and the shop tap is still intact,

have to leave the circuit breaker, boss wants 5 grand for this thing,

 

[CJ]

matching cab has six 12's angled like a folding horn setup,

QC sticker still there,

 

[CJ]

original Mullard 12AX7a has matched sections,

yes the tube tester is from the same company that makes the amps,

10 is right between the stock ax and the hot ones (ecc83s)

 

[metalockpick]

I bought one of these for $125 in 96 (from an LA dealer) and immediately flipped it. No regrets.
These are inexplicably coveted in the stoner rawk scene...
Fender made a "Sunn" reissue that was closer to a JCM800

 

[CJ]

yeah this was supposedly a Marshall Superbass,

need VW Westfalia to haul cab,

there goes the phase inverter

 

[metalockpick]

yes the tube tester is from the same company that makes the amps

Two things on that tube tester:
1) part of the matching involves filament current draw. The temperature in the room has to be the same for all tubes tested for the numbers to matter. Then it's pretty good.
2) This unit is discontinued. Yours seems to be one of the last ones still working. Once it fails, every tube tests bad, and it's a digital issue. After Adrian (orange engineer) has it figured out, I'm going to buy the next version of this.

 

[CJ]

transformer code says 1052

not Pacific XFMR but Transformer Manufactures out of Chicago.

 

[heatwalk]

Worked on a model A (?) earlier this year. Similar vein, certainly their own flavor of build on the inside. Had to go to quite the effort to drill the heads off of the bolts to get it out of the headsleeve. A later era PCB one in recent memory got toasty on the PSU board.

 

[CJ]

primary inductance test on the OPT:

cheater cord sittin at 120 vac 60 hz (plywood with exposed terminals for safety)

simply inject into primary with unloaded secondary, measure series current in milli-amps AC

divide 120 volts by current and you have your pri Inductive Reactance X-L in ohms at 60 hz.

divide by 2 pi and 60 hz and we get

Pri Ind: 220 Henrys

 

[CJ]

UL screen taps at 40%

2.5K to 8 Ohms

terrible frequency response, sec. starts to rise after 1 KC,

by 4 KC we have double the amplitude, loaded or not, wtf?

thought it might be from having the feedback wire still connected but it feeds a 22 K ohm resistor which compared to 8 ohms is not going to resonate with anything

 

[CJ]

sq wave at 1 KC,

you like the beater scope?

 

[CJ]

at 1 KC there is already a substantial phase shift ,

 

[CJ]

at 4 KC a resonant bump occurs which doubles the output signal,

i wonder if this xfmr was copied from a Dynaco tweeter blower that Doc Hoyer told me about?

power transformer is pumping out about 500 V which is about normal,

 

[CJ]

we are raising the input voltage 10 volts per hour to reform the filter caps,

schematic>

 

[Philbo King]

on the bench today is this thing>

Off topic
I had one with two 4x12 speaker bottoms in the '70s playing in a prog rock cover band. Awesome piece of gear, but it gave me an 18 dB hearing loss in one ear. Extreme overkill nowadays.