Heathkit AA100 issues

[hotgas]

I've had this integrated tube amp for a while now but just started to play with it recently. This is a very sweet amp and I can listen to it for hours without listening fatigue if it is working right. Here are the problems.

When I turn it on the left channel is slow to respond. Wait for few munites and play with the balance knob I got the left channel to play. The right channel is always good.

Then I turn the amp off, connect another speaker to the center speaker connections of the amp, turn it on, and the left channel is off again.

So I remove the center channel and only use the left and right ones, but now no matter how much I adjust the balance knob I can't get the left channel to work. Questions:

1) Could the balance knob be the culprit?
2) Do I miss anything? In the back I can see couple wires with hooks which are supposed to tie to something but I am not sure where.
3) Or anything else?

 

[NOSValves]

99% of the time this will just be dirty controls, switches or tube sockts/tube pins. Get a can of Deoxit and give them all a good cleaning. Freshening it up under the chassis with some new parts wouldn't be a bad idea for sure.

Craig

 

[hotgas]

I'd cleaned all and the pot's and switches with Deoxit 2 days ago and just turned it on again today. I also swapped the output tubes but the symptom is still the same. Should I replace the balance pot?

 

[hotgas]

Anybody know where to buy this balance pot? I think this is my best shot to repair as my skill in finding a bad cap is very limitted.

 

[edlipman]

Fading

To find out if the balance pot is bad, disconnect the center lead. This disables the pot. If you still have the same porb. it is now not the balance pot.
Does the amp have pre out and amp in jacks? If so remove the jumpers and try switching the feeds with a pair of rca cords. Does the prob follow or stay in the same channel? If the prob follows the fault is in the pre. , if not the fault is the amp.
Check bias voltages in the amp, between the grid and cathodes, especially the output tubes, if the prob is the amp.
Hope this helps
Ed

 

[NOSValves]

I'll be surprised if its the balance pot. This amp doesn't have preamp in/outs. Have you tried gently working all the small signal tubes in there sockets while the amp is on. Also try turning the RCA plugs in there jacks with the amp on. Do these things with the volume down !

Craig

 

[hotgas]

Thanks folks. I'll try Craig's suggestion this weekend before attempting a shot at the pot. Will report later.

 

[karmen]

i had a similar problem with this amp. i found it to be a crack in the printed circuit board trace on the power amp board at the rear of the amp. turn the amp over and look carefully at all the solder joints and the traces.

 

[tcdriver]

AA-100 connections

Questions:

2) Do I miss anything? In the back I can see couple wires with hooks which are supposed to tie to something but I am not sure where.

Dear hotgas,

The wire near the "A SPKR" needs to be connected to either the 4, 8 or 16 on the terminal strip. If you are running 8 ohm speakers, connect it to the 8 terminal, if you are running 4 ohm speakers, connect it to the 4 ohm terminal. The speaker should then be connected to the "C" and the other terminal next to it. The "B SPKR" should be connected between the 8 terminal and the "C" terminal if you are using a 8 ohm speaker.

On the back of the unit is a "PHASE CHAN A" switch. This was designed to allow one to change the phase of the A Channel speaker so one would have proper phase on the few early stereo records that may have the right and left channels out of phase. When you cleaned the switches, did you clean this one too? I had a unit with a bad phase switch that caused the sound to cut out.

Did you clean the tube sockets. Your problem could be poor contact of one of the tubes with its socket. With the amplifier off take out and reinstall each tube two or three times. This may scrap through oxidation that has built up causing poor contact.

Finally, this is a Heathkit and whoever assembled it may have left a cold solder joint. Do a careful visual inspection and touch up any questionable connections.

Good luck. This is a great amplifier and well worth the effort to get right.

Sincerely yours,

tcdriver

 

[hotgas]

Tcdriver and Karmen, thanks for the valuable info. I will try your recommendations this weekend. :thmbsp: Wish I had more time in this hobby but workload at work is just too much :sigh:

 

[hotgas]

Updates:

1) Tried Craig' suggestions - Turning RCA and wiggling signal tubes did not help. Left channel still dead

2) Tried tcdriver's: I connected the wire to 8ohm as you said. The left channel still dead. However, if I connect the center channel as well then I can hear weak left channel + very strong center channel + the right channel too. This is good sign or not?

Next step. Already cleaned the "PHASE SWITCH" and now waiting for the DeOxite5 to evaporate. Will test again tomorow. Man this amp sounds many times better than a SS NAD int amp I just bought.

 

[glen65]

Im not of the opinion that the balance control is
causing your trouble But if you want to check it use
an ohmmeter. The center terminal or wiper is connected to ground.
Set the control to the center then go from the center
terminal to each side and you should get the same reading.
It should be about 10k per side. If not disconnect it from circuit
and check it again you could have a component throwing
the reading off. If the control checks ok then next check
resistors R36 and 39. These are 10K fixed resistors and
are hooked in series with each side of the balance control.
Check and make sure these are within range. There is a capacitor
and a 100k resistor hooked in series with R36 and 39 each going
to pin 6 of a 12AX7 tube for each channel check them also.
Like mentioned in a previous post check solder connections
especially on the PC board. Dont forget to make sure all the tubes
check ok.

Hope this helps.

 

[tcdriver]

Heathkit AA-100

Dear Mr. hotgas,

On the amplifier chassis there should be four potentiometers located between the output transformers and the aluminum electrolytic filter capacitors. The two topside potentiometers closest to the output transformers are secondary amplifier input level controls for the right and left channels. The primary level control is the control on the front panel labeled "Level". The center terminal of the potentiometers feeds the control grid of the 7199 pentode section (input stage of the power amplifier). The terminals closest to the output transformers are ground. The following test can be used to determine the location of the fault.

1. With the amplifier turned off, connect (solder) a pair of audio cables to the center and ground terminals of each of the secondary amplifier input level controls mentioned above.
2. connect the other end of the audio cables to a line level source.
3. set the potentiometers to their center rotation.
4. turn on the amplifier and listen for sound from the two speakers.
5. If both channels play the same level then the problem is in the preamp section of the unit. If the left channel of the amplifier is still silent or weak the problem is in the output (amplifier) section of the unit.

Based on your results of the above test we will know were to look next.

Sincerely yours,

tcdriver

 

[hotgas]

Quick update.

After cleaning the "phase Switch", re-sockets all tubes, I now can hear both channels. Yes! The problem seems to be due to corosion of these components.

Now it seems the left channel is a little bit stronger than the right. I am not worrying too much about them right now but thinking I may need to check the tubes later. Thanks a lot guys. Very appreciated all the help from you great poeple.

Tcdriver,
I'll try to do your suggestions this weekend. Thanks.

 

[NOSValves]

Good for you glad you got both channels working again. Does the imbalance stay with the unit at all volume levels ? If its only prevalent at lower volumes it can be nothing more then the volume control is not tracking equally on both channels. If it is at all positions on the volume control then its something else. These old amplifiers should be rebuilt or problems are just going to keep surfacing as you use it.

Craig

 

[hotgas]

Hi Craig,

I'd love to rebuild it but I am not that good. What do you recommend as 1st steps for a novice?

 

[tcdriver]

Dear hotgas,

I am glad to hear that you were able to get the amplifier to play in both channels by cleaning the sockets and controls. Since you have both channels working there is no need to follow the procedure I outlined in my earlier posting.

In terms of balance, there are several ways to balance the two channels of the AA-100. Each of the inputs, with the exception of the TAPE HEAD, have INPUT LEVEL controls that can be accessed from the underside of the chassis. These INPUT LEVEL controls can be used to adjust the level and right left balance of signals coming into the preamplifier section of the AA-100. The front panel balance control can also be used to balance the signal in the preamplifier section of the unit. Finally, the two POWER AMPS INPUT LEVEL controls can be adjusted to balance the right left signals.

For initial set up, from the bottom of the chassis, set all nine INPUT LEVEL controls and the two POWER AMPS INPUT LEVEL controls to their maximum clockwise rotations. With the front panel balance control set to its center rotation and the front panel LEVEL (volume control) set to its normal setting, listen for right left balance when feeding the AA-100 with a mono source. If you still hear a channel imbalance try swapping the 7199 tubes in the output stage. If the balance problem follows the tube then you may need one or both 7199’s to be replaced. If the balance problem does not follow the tube switch, then there are other things to look at. If the difference in level between the two channels is small you may simply wish to adjust one of the POWER AMPS INPUT LEVEL controls so that the two channel’s outputs match.

Sincerely yours,

tcdriver

 

[hotgas]

Tcdriver,

Thanks very much for your help. I just listened to the amp today and was very please with its performance. Everything is fine now. The balance pot works fine. I guess the cleaning of the switch did it. This is a such sweet amp and I love it. Now it is time to work on a different project with the recently bought Dynaco PAS2/ST70 combo.

 

[tcdriver]

Pas2/st70

hotgas,

I am glad to hear that your AA-100 is now working as it should. It is a good amplifier and very good looking in a sort of sixties kind of way. :thmbsp:

I think that you will find that the PAS2/ST70 is a step up from the Heathkit. These are great sounding units. Make sure that you add the coupling capacitors to the line level stage just like PAS3X. That will keep the DC from getting to the input stage of the Stereo 70.

tcdriver

 

[hotgas]

Tcdriver,

Where can I buy the coupling cap's? I'd like to hear the system before and after.