TIP31 TIP32 power amp for guitar?!

[PRR]

> The biasing on the output stage of the "Universal Tiger" (Popular Electronics, Oct 1970, p31) is terrible.

The bias was maybe the least of the UT's troubles. (Note that Q7 Q8 idle cold, Q5 Q6 pull the load through R15 R16 until many mA flow in R15 R16.)

They were very prone to oscillate "for no reason". And they were over-volted, low-price, and thus saggy.

Dan Meyer was on the cutting-edge of the one-man in a garage kit boom. The few big-shop designers were not sharing their tricks. Dan had some good ideas, and explained them well (within the tolerance of PE's editors), but he did get ahead of himself somewhat.

[Rob Strand]

The bias was maybe the least of the UT's troubles. (Note that Q7 Q8 idle cold, Q5 Q6 pull the load through R15 R16 until many mA flow in R15 R16.)

The ETI 480 unit had some weird behaviour with R15 and R16 as well.  IIRC, there's a point where no current flows through R15 and R16, and it changes direction.   When driven into clipping it could cook R12 and R14.

They were very prone to oscillate "for no reason".

It's essentially relying on Q3's Cbc capacitance for the pole-splitter.   C8 then tries to give it a bit more lead.
There's a risk Cbc tolerances, or Cbc variation with collector voltage,  could kick it into oscillation.  I'm fond of adding fixed caps to swamp Cbc a bit despite the fact it could be losing bandwidth.

I thought this paper made some good points when I read it back in the 80's.

http://audioworkshop.org/downloads/Edward.M..Cherry.-.A.Power.Amplifier.%27Improver%27.pdf

Dan Meyer was on the cutting-edge of the one-man in a garage kit boom.

Well he certainly pushed out quite a few designs for the masses.   Considering it was the early days of SS amps he did a good job.  It's easy to criticize it today after vast growth knowledge from the 70's and 80's.

[printer2]

They were very prone to oscillate "for no reason". And they were over-volted, low-price, and thus saggy.

The saggy nature was one thing I thought might be good in a guitar amp. The oscillations, no idea but at the time with the screaming guitars it might have been overlooked.