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HK Citation II pushes out speakers when powering off

whosoever

whosoever

New Member
Howdy,

I have a Citation I and II going into Altec Model 19s. I run the amp and preamp off of a variac at 117vac.

When I power down the Citation II, it momentarily pushes out the speaker (Altec 416) to the point where I'm not comfortable using it until I fix the issue. There is no pop sound either. It behaves like this when there is no preamp connected or if I'm running it directly off the house AC power (no variac).

It seems to me that DC voltage is discharging on shut down and flowing directly to my speakers.

The Citation II has the McShane upgrade kit but I'm not sure which level as I purchased this with the work already done.

I just opened it up today and am familiarizing myself with the schematic. I've restored and repaired tube preamps and tube amps in the past but always learning though. I did my Citation I with the McShane kits and am really happy with the result.

Has anyone experienced this issue or could point me to what part of the circuit that may be causing this?

Thanks in advance.
 

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not really any way this could push out DC across the speaker terminals. They are such low ohms that nothing meaningful could develop there. Maybe a low frequency oscillation at power-down could exist though. Not going to claim any familiarity with these or the mods to say if thats happening for sure, or what might cause it.
 
whosoever said:
Howdy,

I have a Citation I and II going into Altec Model 19s. I run the amp and preamp off of a variac at 117vac.

When I power down the Citation II, it momentarily pushes out the speaker (Altec 416) to the point where I'm not comfortable using it until I fix the issue. There is no pop sound either. It behaves like this when there is no preamp connected or if I'm running it directly off the house AC power (no variac).

It seems to me that DC voltage is discharging on shut down and flowing directly to my speakers.

The Citation II has the McShane upgrade kit but I'm not sure which level as I purchased this with the work already done.

I just opened it up today and am familiarizing myself with the schematic. I've restored and repaired tube preamps and tube amps in the past but always learning though. I did my Citation I with the McShane kits and am really happy with the result.

Has anyone experienced this issue or could point me to what part of the circuit that may be causing this?

Thanks in advance.
Click to expand...
Turn the Citation II off before the Citation I.
 
gadget73 said:
not really any way this could push out DC across the speaker terminals. They are such low ohms that nothing meaningful could develop there. Maybe a low frequency oscillation at power-down could exist though. Not going to claim any familiarity with these or the mods to say if thats happening for sure, or what might cause it.
Click to expand...
It does seem like a low frequency oscillation. The cone movement is pretty slow. Probably also has to do with the high efficiency speakers.
 
whosoever said:
I get the same behavior when the Citation I is not connected.
Click to expand...
Does Jim's mod include a bleeder resistor in the power supply? It's usually a 1 or 2-watt, 220k to 470kohm resistor.

That may help bleed off some of the flyback DC voltage (back EMF) from the OPT on shutdown. This flyback, especially in big OPTs, can cause woofer excursion and "thumps."

Some units also use diodes for this purpose.

Bleeder-Resistor-in-Filter-Circuit.jpg
 
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Mr Boochie said:
Does Jim's mod include a bleeder resistor in the power supply? It's usually a 1 or 2-watt 220k to 470kohm resistor.

That may help bleed off some of the flyback voltage (back EMF) from the OPT on shutdown. This flyback, especially in big OPTs, can cause woofer excursion and "thumps."

Some units also use diodes for this purpose.

View attachment 3784058
Click to expand...
I'll check this out as well. Thanks!
 
How does it sound, like a THUMP or like a FART? It’s all dues to the amplifier losing power (but not every tube in your amplifier reacts in the same way).
 
jefferylhenr said:
You have something developing a potential imbalance on power down. If it’s both channels, assume power
Click to expand...
Seems like this is happening on both channels. So the only thing in common would be the main power supply?

98ac2acc-3180-492a-9b85-808cc659ab23.jpg

Anyhow, the original CII doesn't appear to have a bleeder resistor in the power supply. :idea:

Click on the image to enlarge it.
 
Jim's mods significantly increase the capacitance in the main HV and the bias supply. Given the age of some of those parts in there, you might be getting some motorboating at shut down due to a timing issue as the caps drain, or some other kind of instability. Mr. Boochie's suggestion of a bleeder across the HV might be cheap way to see if that alleviates the problem.
 
I'm going to hook up the amp to some old speakers and try to recreate the problem. Hopefully have time later tonight or tomorrow. I know the issue is definitely in channel A but not sure if it is also happening in channel B.

Bleeder resistor sounds like an easy fix but would also like to check all the voltages to see what's going on.

I appreciate the guidance!
 
You should consider adding them and keeping them in place even if it doesn’t fix the issue, it’s safer to work on the unit when the power supply caps discharge upon power down
 
What type of coupling capacitors does the circuit use? If they are old oil-impregnated paper, aka paper in oil coupling capacitors, they may be leaking (:) not oil, but current). You may also notice significant excursion of the speaker cone.
 
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