Quote from: g1 on January 26, 2016, 11:59:27 AM
  To speculate a bit about the etymology of "rail":
in electric railway (and subway) systems, the power is taken from the "third rail".  This goes back over 100 years.

Good point! Same with Lionel toy trains where I got my first electric shock. Really just a tingle from 24VAC.

There was a discussion on MEF a year or so back about a "Split Rail" tube power amp. In that design the screen supply is about half the main B+ Voltage like many of the Music Man amps.

Many semiconductor manufacturers are discontinuing products that have low sales numbers. Frequently it's the through hole version that gets the axe first, OEMs only use the surface mount versions and that's where the big sales numbers are. Some of the new parts that get designed are never made in through hole versions. There are little adapter boards that you can solder surface mount IC's to for prototyping.

Is the Buz 901 part a lateral or vertical FET? The difference being the Source is connected to the case on a lateral (2SK134) and the Drain connected to the case on a vertical. Biasing is completely different too. Unless you can find some laterals, circuit mods will be required.

With no speaker connected, the 4V or so on the output is probably normal for this circuit. It comes from Q2 through the feedback resistors.

Enzo beat me to it ha ha.

Quote from: galaxiex on November 02, 2015, 07:56:42 PM
Slightly OT...
I actually have one of those Heathkit combo amps (Heath TA-16) that is mentioned in the 2nd post of that thread.
It uses that mix of NPN si and PNP ge transistors in the output stage. TA2577 NPN si, 2N2148 PNP ge.

Most of the designs from the mid to late 60's didn't pay much attention to thermal feedback. Many times the bias diodes weren't mounted on the heatsink. A number of designs just used fixed bias like the Thomas/Vox amps. The Si/Ge designs were an attempt at a complementary output stage using parts that were actually available at reasonable prices.

Often times when two pieces of equipment are connected together with single ended cables, a ground loop is created. The amount of hum picked up is highly variable and depends on many factors. Since the 5010 was not intended to receive an external signal other than at the guitar input, there may be significant hum between signal ground and the mains power input safety ground.

One thing to avoid is using the chassis of the 5010 as a ground for the new jack. Connect the jack's ground to a ground at the Master Volume pot on the PCB.

You will probably need to locate and cut a trace on the PCB.

Edit: Bonus feature... Your amp will now have a low level hum.

R13 is not a feedback resistor, it's part of a bootstrap current source load for Q2. It uses the output capacitor and the speaker as the parts you normally see connected to the opposite rail of Q2's emitter which, because Q2 is a PNP, would be ground. A cute circuit that eliminates one resistor and one capacitor at the expense of a little DC current in the speaker. A similar circuit to the one in a recent MEF thread. Look at the last post here, link: http://music-electronics-forum.com/t40551/

The feedback network is R7, C2, and R5.

Ouch, 59MB

The link above redirects me to a page that looks like software sales. WTF??? The authors seem to be the guys who started Audio Precision, makers of audio test gear.

If there is an official AC15 Top Boost schematic, I don't think it came from JMI. Perhaps there is a re-issue or something more contemporary. Here is a link to a thread on MEF where dchange0 cleaned up an AC15 schematic.

http://music-electronics-forum.com/t39856/

Are you sure that is a piezo tank? The second pic shows what seem to be coil bobbins hanging off the bottom at each end.

I'd be tempted to go with the smaller unit. Guitar amps sound better with weaker transformers.

Q1 needs a ground reference for it's Gate. A 1Meg to ground or just short out C4.

Could it be the wacky tone controls? When I first saw this thread I was thinking it was one of the contempory Traynor amps but I re-read the first post and the amp is a YGM3 from the 70's..