ASR-444 Stromberg Carlson: Channel A Deficient Treble After Rebuild

[UncleBingo]

Watching this thread

FWIW, I have an ASR-433 on the bench doing a similar thing. One channel (channel A) quieter. Lacks some bass but the B channel doesn't lack treble.

Improved somwhat after swapping out the 2W 150Ω resistors on the output tubes and a few other caps, but, not right yet.

 

[Grid]

Watching this thread

FWIW, I have an ASR-433 on the bench doing a similar thing. One channel (channel A) quieter. Lacks some bass but the B channel doesn't lack treble.

Improved somwhat after swapping out the 2W 150Ω resistors on the output tubes and a few other caps, but, not right yet.

Yeah, I'm quite concerned. I spent a month rebuilding this. How the hell can this be happening with all new parts, I wonder? Very non-rewarding.

 

[s-petersen]

Have you found anything with the phono issue?

 

[FlaCharlie]

I'm not able to access a schematic right now but if you replaced parts on the tone pots it might be possible that you either damaged the pot or (I forget if it has one) a PEC. It might be a good idea to try bypassing the tone pots to see what happens.

 

[Grid]

I would look at the 47pf cap at the 6U8, A good pic of that channel from the volume pot to the 6U8 would help would likely help

Here are the photos you suggested. I hope I captured enough detail.

 

[Grid]

I'm not able to access a schematic right now but if you replaced parts on the tone pots it might be possible that you either damaged the pot or (I forget if it has one) a PEC. It might be a good idea to try bypassing the tone pots to see what happens.

The pots do have PECs but they are not switched in until the rumble filter is switched on (by pulling out the bass control knob). I'm not expert enough to know how to go about bypassing the tone controls. Is it very involved?

 

[Grid]

Have you found anything with the phono issue?

Nah, dead A channel. Tuner input is OK and will play turntable. I heard the same problem (less treble on channel A).

 

[Grid]

I'm not able to access a schematic right now but if you replaced parts on the tone pots it might be possible that you either damaged the pot or (I forget if it has one) a PEC. It might be a good idea to try bypassing the tone pots to see what happens.

Hello again, here's the S-C schematic.

 

[s-petersen]

There is a phono pec as well as a rumble pec AFIK The dead phono can be tested by touching pin 1 or pin 6 of the 7025 with a disconnected test lead, it will hum if the following section is working.

 

[Grid]

There is a phono pec as well as a rumble pec AFIK

Oh, my, that's all I need. They're such a pain to find the schematics for. I already tried to find them for the rumble filter PECs. forget it. Are you sure? Where and what is it on the schematic?

 

[s-petersen]

The 433 around the phono section has 1, the 444 around the tone control has the other.
Both schematics together make up the 444

 

[Grid]

The 433 around the phono section has 1, the 444 around the tone control has the other

Yes, the PECs on the 444 function as the rumble filter. They are only switched in when the rumble filter is switched in (by pulling out the bass control knob).

 

[Grid]

The pots do have PECs but they are not switched in until the rumble filter is switched on (by pulling out the bass control knob). I'm not expert enough to know how to go about bypassing the tone controls. Is it very involved?

Hey, guess what? I'm glad you asked about the phono input again. Here's what happened. There were those confounded bog done capacitors (10 pf) in parallel with the 2.2M resistors. When I replaced the 2.2M resistors, I thought those dog bones were resistors in parallel; so I did not replace them. I will right now!

 

[s-petersen]

I see what they have done, the 433 is different than the 444 in the phono and tone sections,even though the 433 schematic says they are the same up to the amp, You are correct, I found another schematic which only shows 1 pec(rumble) per channel.
The troubleshooting is the same though.

 

[gadget73]

do you have a signal generator and an accurate voltmeter to actually see what its doing for frequency response?

 

[Grid]

do you have a signal generator and an accurate voltmeter to actually see what its doing for frequency response?

well, i do have a signal generator and a multimeter and a couple eico vtvm's that i have yet to rebuild.

 

[Grid]

Nah, dead A channel. Tuner input is OK and will play turntable. I heard the same problem (less treble on channel A).

Well, I have those 10 pf capacitors in the phono input now. Still no A channel. Dead.

 

[s-petersen]

While in phono inject a signal into the 12AX7 on pin 1 or 6 to isolate the problem, pin 1 is the first section, pin 6 is the second, You can also check voltage on those pins as well. and compare to the other channel. I'm going to bed for a while, I'm on nights for another week.

 

[Grid]

While in phono inject a signal into the 12AX7 on pin 1 or 6 to isolate the problem, pin 1 is the first section, pin 6 is the second, You can also check voltage on those pins as well. and compare to the other channel. I'm going to bed for a while, I'm on nights for another week.

Well, you get your rest and THANK YOU for this test procedure. It's exactly what I've been wondering about. You see, I'm new to tube amps. Before this, I worked on tube radios, and is was a routine procedure to inject signals to troubleshoot. I just didn't have a clue where to inject here. I know I need to learn tube circuit theory.

Another point to mention is, I'd test the amp after replacing each tube's components. I did the 12AX7s first. But silly me had the amp in AUX. Thus I never really tested my work on the 12AX7s till now when I actually connected a turntable. Something tells me I made an error on the A channel 12AX7.

 

[Grid]

While in phono inject a signal into the 12AX7 on pin 1 or 6 to isolate the problem, pin 1 is the first section, pin 6 is the second, You can also check voltage on those pins as well. and compare to the other channel. I'm going to bed for a while, I'm on nights for another week.

Hey! Wake up! I got news for ya! I did the signal generator thing as you outlined. Traced the problem to the wafer selector! The white wire from the RCA jack had come undone from the wafer lug and the .1 uf cap there. However, I'm afraid the deficient treble problem with A is still there. Actually I'm noticing A has more bass too. But I'm really glad to have one less problem, thanks to you.