Help with HH Scott 222-B - V Low Channel A audio

chapps

Well-Known Member
I got a HH Scott 222-B amp that puts out nice sound on one channel, but very low sound on the other.

1. All inputs, in Stereo Mode AND Mono mode.
2. Connecting one channel input in the back (Channel A), causes the same channel to have low audio. Channel B OK in reverse stereo mode, or Mono Mode.
3. Connecting Channel B alone, no audio in CH A in stereo, but CH A has low audio in Mono, or reverse stereo.
4. All tubes are clearly glowing. There are 4 small tubes in a row with conical protectors immediately behind the front face. 3 tubes have a pinpoint glow - tough to find, but def there, and one tube is difficult to tell.

5. On turn on, the red power light takes time to come on - maybe 30 secs or less.
7. 50% of the time, audio will kick in later after red light comes on, but again 30-60 secs and it slowly increases to full - Is this just total warm up time?

Thank you all in advance !
 
Did you try swapping input cables? If you have a problem with your source or it's cables, swapping CH1 and CH2 input cables will reverse your weak channel condition. Next try swapping output tubes, the 6BQ5's. Swap V4 with V104 and V5 with V105. Don't lose track of original orientation, use a Sharpie to number the tubes if needed. If the low channel goes to B, you have worn output tubes. If it stays the same, swap them back. Next try swapping the driver inverter tubes, the 6BL8's, V3 & V103. Did the problem change sides? If yes, you need a new 6BL8. If not, swap them back and try preamp tube swapping, V2 & V102, if that moves the weak channel, you need a new 12AX7. V1 and V101 are Phono section tubes. If you are having a problem only with a Phono input, try swapping those. You long warm up may be due to a worn rectifier, 5AR4 tube. You need a tube tester or another known good 5AR4, even a 5U4 or 5R4 will do for testing, just don't expect the same output volume overall. You can mail me your tube set for evaluation on my TV-7D/U, no charge. I have several tube amps for real world evaluation of most of your tubes and replacements for worn out ones, too.
 
Chapps,
First thing to suspect is a tube problem. The time lag to pilot lamp and sound output is normal--that's your 5AR4/GZ-34 tube rectifier warming up. B+ voltage doesn't get to the tubes until the rectifier warms up and starts conducting. Gives your amp a nice 'soft start' feature. The volume may rise some while the tubes are still warming up, even after sound has started to come out of the speakers.

I'm not sure I'm following your description, but are you saying Channel A is always low, regardless of input set up?

The four small tubes in front with the shields are your phono pre-amp tubes (1 for each channel) and line amp/tone control tubes (one for each channel). These are all 12AX7 dual triodes and they don't have a strong glow--you have to look to see them. The four tubes nearest the transformers are your 6BQ5 output tubes (2 per channel). The ones in between are the 6BL8 driver/phase inverter tubes (one per channel).

Do you have the ability to test the tubes? If so, do and see if you have a bad one.

If not, you may want to swap the pairs of tubes, starting with V1/V101 (pre-amp tubes), V2/V102 (line amp/tone control), V3/V103 (driver/PI) to see if the bad channel moves with the tubes. If it does, you have found your bad tube. If that doesn't do it, try swapping the output tube pairs of V-4 & V5 with V104 and V105. Let the tubes cool a bit between swaps and, of course, have the amp off when changing tubes. If the problem exists on the high level inputs (AUX and TUNER) it's probably not the pre-amp (PHONO MAG INPUT) tubes.

If it's not the tubes, then you may have another problem that needs to be dealt with. Is there any hum/buzz present? Are any of the output tube plates glowing cherry red or even bright orange?

Dave
 
Whoa ! Whoa! Newbie here, slow !! slow !! :biggrin:

Thanks Kev, for the reply.
OK. ....problem on Extra, Tuner and Tape inputs. Not tried phono.
1. V4, V104 etc.....so I downloaded the schematic. I can see the numbers...so that I can try.
2. "Don't lose track of original orientation" - you mean each tube should go back into its original socket, right?
** So tube glowing does not mean fully functional?
3. Inverter tubes...OK I see those - will try and report back.
4. Preamp tube swapping - so the preamp controls all inputs?? (Dont laugh !!)
5. I have not tried phono input yet, so will leave that for later.
6. Ok I see the rectifier tube - is it just better to replace without testing.


Can I just send you the amp?? Happy to pay you whatever.:)
 
And thanks Dave too !

"I'm not sure I'm following your description, but are you saying Channel A is always low, regardless of input set up? "
** Yes. Is low on all inputs. Also, on reverse stereo (for sure), or mono (if I remember correctly). So it is a output thing?

""These are all 12AX7 dual triodes and they don't have a strong glow--you have to look to see them.""
** Yes tiny pinpricks of light. But I have not tried phono yet.

""Is there any hum/buzz present?""
** No hum. Very clean silent on the playing channel, and no hum on the low channel even at high volume.

"Are any of the output tube plates glowing cherry red or even bright orange?"
** Didn't know there were color options ! Just kidding.
I am not competent to tell that there is any difference.
 
Back
Top Bottom