Maker Pro
Maker Pro

Heathkit TA-17 Amplifier

Bart Rydzynski

Apr 14, 2016
39
Joined
Apr 14, 2016
Messages
39
With R113 removed, the BASS channel is isolated except for the common 60 volt supply. Oscillation (squeal or motor-boating) requires uncontrolled in-phase feedback from output to input of an amplifier stage. Was the amp properly working when you bought it? Possible sources for feedback include wiring error, solder bridge, insufficient de-coupling of the power supply or creative rewiring of the amp..... the later possibly creating ground loops, inductive coupling or a high impedance path to the power supply filters. The fluctuating voltages indicate an unstable bias or voltage source.The transistors are DC coupled and they all interact. You may have a thermal problem with one of them. Have you used freeze spray on semiconductors before? You are getting close to needing a DC coupled, dual trace oscilloscope. Without knowing the history of the amp, I would first make sure there are no solder bridges. Next, check for wiring errors and make sure all the components are of proper value. Then check the 60 volt power supply to make sure there are no fluctuations.. Also, keep the GUITAR and MIC channel pots on zero.
 

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
Thank you Bart. Sorry for the delay as I was away. Back to the AMP... so now I have a problem with Q14 yet again.

Q14B = 37v
Q14E = 37v
Q14C = 15v which should be .45

R317 (47ohm) has burned again... I had this problem before.
I removed the B wire from the board to isolate... Q14C still 15
I checked the voltage on Q12C which is 37

If you recall the original problem with the amp was burning resistors

R315 (100ohm)
R317 (47ohm)

Truly stumped again but will keep trying and start from the top.
Voltages from Q12, 13, 14, 15, 16 - will report back.


thanks
Ron
 

Bart Rydzynski

Apr 14, 2016
39
Joined
Apr 14, 2016
Messages
39

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
Hi Ron.
Pull Q12, 13, 14, 15, 16. Test them for gain and leakage. DO NOT REINSTALL.
Power up amp. C604+ (4000/50V) should be 0 volts.
Measure C503+ (8000/90V). Should be 80 Volts.
Check Q10, 11 for proper volts.
Turn off amp and allow C503+ to bleed to 0 volts.
Check R620, 621.
Check D601, 602.
Check D301, 302.
Check any remaining suspect parts.

Will do Bart. Aside from my transistor tester, when you say check the transistors for Gain and Leakage, what is the right way to do that ?

Many thanks.
Ron
 

Bart Rydzynski

Apr 14, 2016
39
Joined
Apr 14, 2016
Messages
39
Your tester will do it automatically and display the results. I think you have to scroll the screen to view all the test results of all test perimeters.
 

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
Bart, sorry for the delayed response. I have been busy fixing the circuit card which as it turns out had many really bad pads. I have a video series on this amp that you can watch here to see what I am up to. Episode 14, 15, 16, and 17. I have repopulated the entire board and am reinstalling it at the moment in the chassis. I think it will work perfectly when I am done.

I will keep you posted. Thank you for sticking with me on this.

Thanks
Ron
 

Bart Rydzynski

Apr 14, 2016
39
Joined
Apr 14, 2016
Messages
39
I admire your determination. I'm keeping my fingers crossed!!
Waiting to here some Who through it. :)
BTW.... great series!!
Bart
 

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
Bart - I made a huge discovery today... its in this video.. basically, I think I know why R317 (47ohm) was melting.....
The bridge Rectifier was grounded to the circuit board instead of the chassis... effectively the first component in the part is R317 :)


:)
 

Bart Rydzynski

Apr 14, 2016
39
Joined
Apr 14, 2016
Messages
39
Hi Ron, Don't forget there are three more ground wires attached to "CT". A circuit board ground, speaker ground and a ground to Q16-E.
 

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
Hi Ron, Don't forget there are three more ground wires attached to "CT". A circuit board ground, speaker ground and a ground to Q16-E.

Yes agree. I think though having the terminal strip not connected to the chassis at that point potentially can cause issues other places in the unit.. I could be totally wrong but I think the chassis ground in that spot has some significance. who knows..

Thank you Bart :)
 

Bart Rydzynski

Apr 14, 2016
39
Joined
Apr 14, 2016
Messages
39
Hi Ron, A jumper at CT makes the chassis a common ground reference point. It's primary purpose is to add shielding to the high gain amplifier stages/wiring, reducing hum and extraneous noise. It also reduces the chance of internal oscillation.... squeals, chirps, motor-boating, etc.. The jumper is mandatory for proper amplifier performance.
 

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
Hi Ron, A jumper at CT makes the chassis a common ground reference point. It's primary purpose is to add shielding to the high gain amplifier stages/wiring, reducing hum and extraneous noise. It also reduces the chance of internal oscillation.... squeals, chirps, motor-boating, etc.. The jumper is mandatory for proper amplifier performance.


Thank you Bart. If you recall, that was a problem I was having ( Motor-boating, squeals, etc) so I hope this fixed at least that part. I've learned alot on this one, thank you.
 

73's de Edd

Aug 21, 2015
3,613
Joined
Aug 21, 2015
Messages
3,613
.


Sires Bart and Ron . . .or . . .Ron and Bart . . . . . . .
(All in accordance as to who receives top billing )

And there I was . . .doing my dutiful tuning in on the " Ron and Bart Show" with "youse guys" TIRELESSLY plugging away at the recurring and endless problems at hand.
Ever making some forward progress.

I was going to make some references to problems being apparent, but I see that the Pee Cee Bee is now stripped. ! . . . . .naked like . . . no less.

Looking at probably your worst case on that PCB . . . . can I fill you in on my rework process ? . . . It's bordering on Mil Spec-Aerospace and NASA quality standards . . . . being increasingly perfected upon, during my 60 year PCB learning curve.



Your PCB's probable worst area and the potential / resultant rework is down at the very bottom photo.

Photo . . . . . as excerpted from your HEATHKIT pcb
vwoT4iL.jpg







If interested ? . . . . Fill me in.



73's de Edd




.
 
Last edited:

Ron Cianciaruso

Apr 14, 2016
54
Joined
Apr 14, 2016
Messages
54
73's de Edd... I indeed did have to do alot of repair work on the PCB and have confirmed and certified it is now back to a usable condition although surely not Mil Spec. I like your work on the photo's... do you do that for a living ? Very very cool.. The area you have highlighted has been repaired and fixed much like your drawing.

Regards Ron

P.S. Bart has been a lifesaver to me.. he has taught me so much, its amazing. A really nice guy !
 
Top