Acoustic 150 Question

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here is a new voltage chart,  my mistake was not noticing that the rail voltage was dropping as things got hot, thus the V-eb error,

 

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> 40410 is PNP si  T05 in a welded heat sink.

I'm old friends with the '410 but thanks! for the resume.

> If the amplifier is working, why look @ making any changes.

CJ's numbers suggest R311 is sitting with 47V across 560r which is just about 4 Watts in a 5W part. An *old* 5W part.

There's also the number-game suggesting C303 may be leaky.

I'd be scared that CJ takes dude's money, R311 smokes or C303 shorts soon after, dude is upset.

On fourth(?) thought.... the power stage may have power gain as low as 20dB. So if this is 150W output, we need 1.5W drive. Since this is class A driver, we expect 3 Watts in the driver power device. CJ's voltage chart shows 21V 83mA or 1.8 Watts at 250r. The factory numbers say 37V 61mA or 2.2W at 600r. The power input is only a hair different (due to clever fail-safe bias) but the impedance difference is substantial. Even allowing for the w-i-d-e impedance swings of a B-E junction reflecting the wide impedance allowance of a loudspeaker.
 
it's like esp (see photo)

luckily this amp is from the shop's bonepile,

people in this town like the retro stuff, so it will sell fast once it hits the floor,

going to pull RCA and bench test it,

maybe double up the resistors for 10 watts and circa 1K ohms to limit current, if a new transistor does not fix things,

not that many changes being implemented, the amp still rocks, just some new output transistors (ON-MJ15003G)
and filter/output cap,

wondering what the OEM part number crosses to RCA 48-15) , probably 2N3055 back i the day,
 

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ok the heatsinked RCA is leaky, shows good on the diode check EB and CB but E to C reads1.5 K ohms both ways, should be infinite,

these can be had on ebay but not digikey,  i believe Peavey used these also, they come in comp pairs IIRC,

why did it go bad? probably because engineers did not design for stomp box abuse back then, put a fuzz face in front of the 150 and it will get a workout,
 
that might be a good idea,  we will crank this thing into a 4 ohm load and see how it does,

that innerstage transformer will like the reduced DC once we get a new driver in there,  even though the core seems to be more than adequate,
 
Hi CJ
The 48-15 or 480015 is a special RCA 2N3055 Hometaxial with our house number. It is a 90 volt part that we ran an incoming test to sort out bad devices. My incoming test fixture was a 80 volt supply and 1.2A and a small 4" square of 0.062 alum, socket and thermal probe. The transistor was inserted, clamped, power on, thermal reached 100C, power OFF, the part was good.This tested for Isb & Thermal bond. Jack Sondermeyer was my RCA man @ that time and we had many talks about this test. Jack later left RCA and went to Peavey. I told Jack that in LA we seperated the men form the boy. The die bonding has air bubbles and Isb problems created hot spots burned up the devices.

Don't replace this part with a new 2N3055 as most of them are Epi base types and Ft will cause stability problems.

The output power is about 80-90 Watts and not 150 Watts.  Back then marketing was very liberal with specs. I have many stories just like JR has.
Duke :)
 
Audio1Man said:
Hi CJ
Jack Sondermeyer was my RCA man @ that time and we had many talks about this test. Jack later left RCA and went to Peavey. I told Jack that in LA we seperated the men form the boy. The die bonding has air bubbles and Isb problems created hot spots burned up the devices.

Don't replace this part with a new 2N3055 as most of them are Epi base types and Ft will cause stability problems.

The output power is about 80-90 Watts and not 150 Watts.  Back then marketing was very liberal with specs. I have many stories just like JR has.
Duke :)
Jack Sondermeyer was another New Jersey boy.  Hartley recruited Jack to make Peavey power amps that didn't blow up, and he succeeded famously at that. 

I used to co-present a  dealer seminar with Jack (the Jack and Johnny show). I'd introduce him as having forgotten more about power amp design than I ever knew, and I was only half joking.  8)

He is missed. RIP

JR
 
yes that CS800 monster amp is still in use today, people love those amps because they never break, sound good and are built like a battleship,

we popped the RCA 40410 out and soldered in , very carefully as to not open the collector lead or have the can explode, a Motorola 5415 PNP, Ic-1 A, Vec 200, hfe 30 to 150 in its place,
 

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as long as we are under the hood, why not check out that xfmr,

EIA code says Marvel Electric from Chi Town

http://www.marvelelectric.com/

DCR 45 ohms pri  about 3.4 each sec,

75 EI butt stacked 29gaM6,

probably wound pri-sec-pri with the sec bi-fi as mentioned earlier,

Ratio:  6:1+1
 

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very good transformer,flat to100 KHz, very little ring, 

here is a pri-sec sq wave shot at 100K.

 

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what good is a freq plot without a complete tear down?


exactly.  :D

so a shot of the thin gap paper?
 

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could be watching Efren Reyes torture Earl Strickland on youtube right now, but no, not until the obsession has lifted,

looks like the finishes are grn/blk and yel.  makes sense as we need a phase flip for push pull,
 

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random wound at 40 turns per layer,  except last layer which was 30T.
 

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was wondering what insulation build between the pri and sec would give such a good freq response,
low and behold the answer is none!

not a lot of voltage differential at this circuit location, so breakdown not an issue

coil structure is simply pri then the bi-fi sec 

the secondary is 190 turns  each  red and green 

looks like #27 or #28 AWG,  going to reuse the sec wire since it is big enuff and spool on 1140 turns of #30 for the primary,

1140/190 is a turns ratio of 6:1+1 as read on the volt meter, the close proximity of pri/sec means good linkage thus the turns ratio closely matches the voltage ratio,
 

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this is what 40 turns per layer looks like with #30,

spaced out wires = good freq response,

lowers C from turn to turn?

probably lowers C by putting more air between layers as the wire crosses over at an angle which prevents it from sinking into the valleys,
 

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> lowers C from turn to turn?

C should be a non-issue on these low-Z windings. Even 1,000pFd self-capacitance on ~~600 Ohm primary is 1/4 MHz.
 
CJ I like the work you have done on the driver transformer. The driver is RCA 40410, not 40401. You have incorrect several places. The family is RCA 40406, 40407, 40408, 40409, 40410 & 40411 were used in several Acoustic products.
Duke :)
 
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