Heathkit TA-17 Amplifier

[Bart Rydzynski]

You have a good opportunity to learn from this problem. You theorize what the problem is and it's solution. Pull Q6 and see if the results match your theory. Yes? Great! No? Why not?

 

[Ron Cianciaruso]

I now understand a little more here. The X29a829's I bought to replace the originals indeed did have different layout of the pins... They were EBC.... so I removed them all and replaced them with the originals.

The 2N3391, 2N3859A and the 2N3393 seem to be the same package.

With all the correct parts in now, the guitar still has low volume and distortion in the guitar jack.
In the Mic jack I've adjusted things to your suggestion and it seems slightly distorted
The Bass Jack is not working at the moment, and i see I still only have 8-10volts C103.

I am thinking that since I have had such wild voltages flying around this thing, the best bet is to get all new transistors ( The right ones) and see where I land. I think I am close here....

Make sense ?

 

[Ron Cianciaruso]

You have a good opportunity to learn from this problem. You theorize what the problem is and it's solution. Pull Q6 and see if the results match your theory. Yes? Great! No? Why not?

Pulling Q6 had no bearing.. see my last post

 

[Bart Rydzynski]

Replacing all the transistors may be your best bet since you do not have a transistor tester and cannot verify their performance. If you continue and enjoy working on transistor circuits, you may want to look into a transistor tester for your work bench. It will pay for itself in aggravation saved the first time you use it.

 

[Ron Cianciaruso]

Replacing all the transistors may be your best bet since you do not have a transistor tester and cannot verify their performance. If you continue and enjoy working on transistor circuits, you may want to look into a transistor tester for your work bench. It will pay for itself in aggravation saved the first time you use it.

Very good advice on the tester. I am going to order the transistors now and will report back when they arrive and I get them installed. You've taught me a great deal so far I am sincerely appreciative of your time. Have a wonderful week Bart.... and thank you !

Regards
Ron

 

[Bart Rydzynski]

My pleasure. I really enjoy helping you because you have an eagerness to learn. Will be waiting for your next update. You too have wonderful week!
Regards,
Bart

 

[Ron Cianciaruso]

My pleasure. I really enjoy helping you because you have an eagerness to learn. Will be waiting for your next update. You too have wonderful week!
Regards,
Bart

Parts are ordered and I also ordered one of these DCA Pro testers... Good stuff.. this will help me tremendously as I do more work with transistors ( Which I love)... thanks

 

[Bart Rydzynski]

Good choice. I've heard good things about this tester.

 

[Ron Cianciaruso]

Bart - A question.
In my quest to find the correct X29a829 I came across a BC640TA which appears to have exactly the same properties as the X29A829 ( PNP 80V 1A to TO-92) and on the data sheet the PINS are correct for this package. I tried using NTE159 but they have the wrong pins as described yesterday.

Some Heathkit sites say to use the 2N3806

Since I am a transistor newbie... is the BC640TA ok in your opinion ( I did check the data sheet and it looks right to me). Thank you again

 

[Bart Rydzynski]

???.... couldn't find any data on the BC640TA or X29A829. The 2N3806 has a max collector current of 50 mA, and the NTE159 has a max collector current of 800mA. The NTE159 is more robust in this respect. I've used NTE devices for years and swear by them and would be my first choice. A 2N3906 would be my second pick. Rearranging the leads on the NTE159 to fit the board is no problem.

 

[Ron Cianciaruso]

Thanks Bart. I will go with the NTE159 on this and spin the package around to get it to align.
Here is the data sheet on the BC640TA for reference.

http://www.mouser.com/ds/2/149/BC640-888547.pdf

thank you again

 

[Bart Rydzynski]

OMG! Mouser is my number one source for parts but I didn't check with them. Go figure. Thanks for the link. The BC640TA looks to be a good sub and is certainly worth consideration. A quick note on transistor subs: Generally, you can make an educated choice on a sub by reading the data sheets. Oscillator circuits and RF amps can be extremely touchy and require an exact replacement. I once had a shorted RF transistor that I replaced with a NTE replacement. The amp still did not work. I spent several hours working on the thing before I finally consulted NTE's data sheet. It clearly stated "This device may not work in all circuits". I installed an exact replacement transistor and the amp worked as intended. The embarrassing part was a co-worker warned me NOT to use the NTE part. Lesson learned.

 

[Ron Cianciaruso]

Good evening Bart. I have a mystery on my hands. I received all the new transistors, tested them, checked the config and installed them all. Guitar Channel words but distorted. Mic channel works and I can control the distortion in the way you described earlier. The Bass channel has nothing. I checked C103 and have 60v on the + side when it should be 24. Checking Q4, Q5 and Q6 I do not have the correct voltages.... now the mystery.

While checking around I see R110 on the schematic listed as 10K. Printed on the circuit board it says 100K. I have previously replaced the resistor with a 100K and am wondering if there was a field bulletin on R110 being printed incorrectly and I need to put in a 10K instead. I am hesitant to change it now as I do not want to start blowing out transistors again.

Would you know from experience if sounds off. 100k does seem kind of high in that circuit config, but I defer to your expertise. Thank you sir..
Ron

 

[Ron Cianciaruso]

Good evening Bart. I have a mystery on my hands. I received all the new transistors, tested them, checked the config and installed them all. Guitar Channel words but distorted. Mic channel works and I can control the distortion in the way you described earlier. The Bass channel has nothing. I checked C103 and have 60v on the + side when it should be 24. Checking Q4, Q5 and Q6 I do not have the correct voltages.... now the mystery.

While checking around I see R110 on the schematic listed as 10K. Printed on the circuit board it says 100K. I have previously replaced the resistor with a 100K and am wondering if there was a field bulletin on R110 being printed incorrectly and I need to put in a 10K instead. I am hesitant to change it now as I do not want to start blowing out transistors again.

Would you know from experience if sounds off. 100k does seem kind of high in that circuit config, but I defer to your expertise. Thank you sir..
Ron

Clearly the install pages show R110 as 10K, so I have changed it... however no change. My sleuthing skills will continue to dig until I find the culprit - Thanks

 

[Bart Rydzynski]

Hi Ron,
My schematic shows R110 as 100K. Assembly picture also shows R110 as 100K. I have a production run change order dated November 19, 1968 and no change (at this time) was made to R110. Is the part number on the circuit board 85-188-1 or 85-188-2?

60 volts on C103+ indicates Q6 is not conducting. Q6-B should be very close to 600 mV. What are the voltages on Q4-BCE, Q5-BCE, Q6-BCE?

 

[Ron Cianciaruso]

This is what I have on Page 7 for R110
https://pbs.twimg.com/media/Cgh4BJNWYAAeMv-.jpg:large

And here is my schematic.
https://pbs.twimg.com/media/Cgh4UP3WgAEE39Y.jpg:large

I'll take voltage readings on the other transistors and report back.

 

[Ron Cianciaruso]

This is what I have on Page 7 for R110
https://pbs.twimg.com/media/Cgh4BJNWYAAeMv-.jpg:large

And here is my schematic.
https://pbs.twimg.com/media/Cgh4UP3WgAEE39Y.jpg:large

I'll take voltage readings on the other transistors and report back.

Q4B = .63
Q4C = .047
Q4E= 0

Q5B=.047
Q5C= .72
Q5E = .73

Q6B = .72
Q6C = .50
Q6E = .46

Clearly wrong on all counts.

 

[Bart Rydzynski]

C103+ has 60 volts and Q6-C has .46 volts? Check the resistance from the + lead of C103 to the lead of Q6-C. It should be less than one ohm.

 

[Ron Cianciaruso]

C103+ has 60 volts and Q6-C has .46 volts? Check the resistance from the + lead of C103 to the lead of Q6-C. It should be less than one ohm.

Good News.. I've solved the voltage issues... The Q6E circuit trace was lifted ( from too much soldering I fear) and there was no connection. I have fixed the pad and reinstalled the transistor and have proper voltage now.
I still have the 10K resistor in there - do you think I should go back to 100K before I cause other damage ? The board does say 100K but my book says otherwise.

Thanks for your help on this voltage issue, but glad I was able to find it and fix it ( with your encouragement ) .
I need to start thinking about the LDR as well and what I will use.. at any rate, allow me to test this thing out and check voltages throughout and I will let you know what else I find.

Thanks again Bart - be back to you.
Ron

 

[Bart Rydzynski]

Did your manual come with your amp? If you bought the manual separately, it may be for a different production run and that could account for the difference of R110. R110 and C102 are for frequency compensation so you can ignore them for now.