Ampeg B 15 N

[CJ]

probably gonna stay away from that microwave food, that stuff kill you quicker than a bullet,
only thing it's good for is a hippy, when their high on weed,  ;D

transformer installed, needs some black tar clean up, maybe some flat black rattle can,

RCA 6L6, and original Ampeg labeled 6SL7's made by Sylvania,

6SN7 tubes work well is this amp also, believe it or not, (gain of 20 compared to 100)

this thing has been sitting for 25 years waiting for a transformer, main filter can ok,

 

[CJ]

you can see the green color of the Lucite logo plate from the side only, looks clear from the front,

 

[CJ]

tube cage on, ready to rock,

Ampeg came out with a later version that had the screen too close to the tubes, pissed of the original engineer, got so hot you could fry an egg on it, corporate wigs trying to save space and money,

 

[CJ]

one final pic before we button her up, took off flat washer on term board, too close to  B+ 22K resistor body,

notice wood strip under board for the stand off,  used yellow vinylglass  over the 5 volt wind, no splice, just magnet wire coming out of the can,

 

[CJ]

OPT sq wave shot, secondary

 

[CJ]

better at lower f ,

OPT has pri DCR of 256 Ohms, split perfect into 128 ea, so we probably have a 3-4, 

4 primaries which sandwich 3 secondaries, maybe about 1200 turns each into a 109 turn 16 ohm wind, and maybe a 77 turn 8 ohm

 

[CJ]

this thing goes all the way to 1 M Hz, with a few peaks and valleys,

wicked sq wave at 50 k

 

[CJ]

sine wave phase shift at 10K, don't have a scope with a computer inside,  looks like about 17.5 degrees, 

 

[CJ]

at 50 K we get a little shift and a little amplitude deviation, but still pretty flat,

 

[CJ]

that looks like about 60 degrees, what do you think?

 

[CJ]

looks like this flip top flips it's top at about 300K,

transformer core is probably the same as the pwr trans since the can is the same size,

125 EI, 2 1/8" stack,

22:1 ratio into 16 ohms = 7.7K P-P to 16

625 Henries at 60 Hz, 120 V-rms,

so probably 1000 H at 20 Hz,

Flux:  1.25 tongue by 2.125 stack = 2.65625 in^2 = 17.137 cm^2

100,000,000 E/4 * 20 Hz * 17 * 2400 turns =  100,000,000 E / 1360 * 2400 = 100,000,000 E / 3,264,000 = 30.6 E

so at 250 V-rms we have 7.6 K Gauss, loafing along,

400 V-rms = 12 k G, no wonder people like the bass coming out of the tuned baffle board, ok then...

 

[Gene Pink]

I think there are some microwave ovens with a rotating metal vane that breaks up the standing waves for less hot spots and more even cooking.

A microwave-size Leslie 122? 

 

[walter]

stand by sw gnd goes into speaker cab then back out, wtf?

amp also hums if you use grounded spk jack on chassis for testing,  have to use cable,

Prevents power on when speaker is disconnected. Early versions used the flip clips for speaker,  but if the clips got loose or corroded the speaker would cut out!

 

[JohnRoberts]

Prevents power on when speaker is disconnected. Early versions used the flip clips for speaker,  but if the clips got loose or corroded the speaker would cut out!

Some tube amps are unstable without a speaker load... It seems a RxC to ground should cure that but I am not a tube guy....

JR

 

[trobbins]

CRO doesn't have X-Y ? 

Did you get a chance to measure PP inductance at low VAC (circa 5 V) for comparison with other OT's ?

 

[CJ]

break down the spk cable>

 

[CJ]

trobbins, we did get some additional data points at 60 Hz, you could extrapolate down to 5 volts,

domains are starting to wiggle but not much,

 

[trobbins]

Yes I can see that measuring 100uA of inductor current with 10VAC excitation is starting to get down to nice lab grade multimeter region, even if using a sizeable sense resistor. 

I was just interested in comparison with the Williamson amplifier type benchmark back in the late 1940's of exceeding 100H at 5VAC - at that time an AVO 7 just showed some meter movement on the 10mA scale.