hi guys , new-ish member here with a recently purchased HH IC100 amp circa 74 -75.
Amp has been working fine for long periods and is out of the shell just now for a clean and visual inspection.

The power amp board is AO3103/7 variant with two [driver i think?] heatsinked transistors numbered BD711 [ uppermost] and BD712.
Earlier on i tried a treble booster through the amp at low volume and saw smoke from the power board and amp stopped working.

Fuses all ok but noticed R26 [ 10 k ] and R10 [ 100r ] looking burnt so replaced them and amp is now working again.

However , the transistor near these resistors numbered BD711 is getting really hot even after just a short time of playing.........it's lower twin BD712 is very cool in comparison.

Can anyone with experience of these amps advise what the problem may be ?
many thanks !

hi guys , just looking for some pointers and help to try and get this amp going again....
im not a tech and just have some limited know how [ can solder and use a meter etc ] but ill list some symptoms which may help you to suggest some areas for me to look.

for a while , the amp was starting to build up a hum when on for about a half hour or so. the hum got grradually worse and louder the longer the amp was on.

so , i changed main filters 4700uf 60v but no difference.

i then turned her up loud to see what happened and she went nuclear with the hum and then i got no signal just hum even with volume off. amp lights up etc but just hums loudly.

i then tried the speaker cable for voltage and got about 40v there.

so , i got a new bridge rectifier bridge KBPC35-06 and popped it in but this didnt cure it and i still have the same issue

while it was still working , i took some readings on the transistors on the power board but not the two main power transistors as i could not reach them.

Q1  - 2SD381,         b -47v c -0v e - 0v
Q2  - 2SB536,         b - 1v  c -47v e - 48v
Q3  - BC204B,         c - 47v b - 47v  e-48v
Q4  - BC207B,         c - 1v   b -0v   e - 0v
Q5  - BC204B,         c - 0v   b -0v   e - 0v
Q6  - 2SD381,         b  -1v   c - 47v  e - 0v

any ideas gentlemen?
many thanks for any help
cheers - bob [ in UK ]