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harman kardon citation ii

M

maciek

Active Member
Hi, I am back with hk II issues, completed all updates of Jim level 2 and resistors, but have v7 and v9 redplating on start ,manipulating bias pots does not help,also meter stays put,any clues anybody?say thank you for any replay:drool:
 
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maciek said:
Hi, I am back with hk II issues, completed all updates of Jim level 2 and resistors, but have v7 and v9 redplating on start ,manipulating bias pots does not help,also meter stays put,any clues anybody?say thank you for any replay:drool:
Click to expand...

First off you need to go over your work to double check. If you know somebody that is knowledgeable have them go over after you do. Obviously something didn't get back together right.
If you got the level II from Jim why not contact him? Believe me nobody knows these amps better. He is always willing to help.
 
Does level 2 deal with coupling caps on the tubes in question? Red plating is caused by too much current through the tubes. If the bias is too positive (not a large enough negative voltage) that can cause red plating by drawing too much current. Leaky coupling caps can be one source of that.

Shelly_D
 
Coupling caps are new recently replaced and were ok before upgrading,could be bad resistors? But just that pair redplating
 
Can't do that right now,I'm at work,which voltages and where, also manipulating bias pots of redplating tubes is not stopping it,
 
Nor will it, the pots on anything will control a small amount of current adjustment but if it's a measurement that is off the map you need to get it under control first. What tubes are you running, kt88's are assumed? You want to measure pins 3 and 8 of the socket with tubes installed. Also check the resistors connected to pin 8, should measure 15ohm. You'll more than likely find that the voltage is higher on the side that's replating, this is assuming it's not a tube issue. Check your grounds as well.
 
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maciek said:
Can't do that right now,I'm at work,which voltages and where, also manipulating bias pots of redplating tubes is not stopping it,
Click to expand...

The important pins would be:

Plate - pin 3
Screen - pin 4
Grid - pin 5
Cathode - pin 8

Take the voltages on both channels and post them showing the good channel VS the bad. It will help us determine where to look

Don't forget to go back over the work you have done on the modification.

Shelly_D
 
Replating on only one set of tubes - the same channel I assume - means a likely wiring error since the other channel is working ok. Per the other posts, focus on measuring bias voltage at the grids of the 2 sockets on the offending channel with the tubes removed. It should measure what the other 2 tube sockets report. If not, there are wiring or connection problems.

Not having kept up with the project, what was the state of the amp prior to the Level II installation? Coupling caps were replaced but what else? Bias circuit rebuilt? What about the grounding rework Jim recommends?

Cheers,

David
 
Entire amp got Jim's upgrades level 2,ground bus installed,new bias,Russian caps,all resistors replaced.After just replacing coupling caps played perfectly.One other thing thing I need to mention,while screwing trafos back on to the chassis bias switch board snapped in half and I had to glue it together and work on it, could be something wrong there?Manipulaitng bias pots doesn't make meter to move at all,only moves on ac balance pots,
 
Ok, then along with Dukiedook's pithy observation ;-), suspect the switch arrangement. I don't have a schematic in front of me so working from memory, here. If 2 of the tubes - no matter the channel - are working ok, then the bias voltage is likely correct but needs to be confirmed with a volt meter - not the meter on the back of the amp.

How comfortable are you with a volt meter? Suggest you start by confirming that the switch now connects things as called for in the schematic. I suspect this is why the meter isn't indicating anything. Also, depend on your own volt meter for idle current measurements rather than the meter alone. I assume you have installed the cathode resistors Jim calls for as part of the upgrade?

Cheers,

David
 
PS kit

1. (2) 820 uf 250 volt 105 degree Celsius very low ESR clamp mount caps that increase the capacitance from
100 uf total in the doubler to 410 uf. (2) clamps are included.

2. (4) General Instruments fast/soft recovery diodes that replace the existing top hat diodes. They fit nicely in the
fuse holder right where the old top hats are now. The GI diodes are very good, and quite reasonably priced too.
If you increase the capacitance, you really need to replace those diodes. And the DO-41 packaging is ideal for replacement.

3. (1) JJ 100/100 dual section 500 volt clamp mount cap, and...

3a. (1) Panasonic 220 uf/500 volt clamp mount cap. The Panasonic replaces the 40 uf 525 volt original twistlock,
and the JJ replaces the dual 50/50 V1/V4 decoupling cap. (2) clamps are included.

Note: This amp responds very well to improved decoupling of the input 12BY7A tubes!

4. (1) .01uf high voltage film cap to replace the existing ceramic unit.

5. (1) Gen'l Instruments fast/soft recovery diode to replace the bias selenium rectifier

6. (1 ea.) 220uf and 100 uf radial electrolytics, a new 1.8K ohm resistor, and a terminal strip for the bias circuitry.
Two new 4.7K ohm resistors to increase the range of bias adjustment


Level II kit

(1) 50uf/50uf F&T German made dual section cap, to be added in parallel with the new C2a & C2b. This raises
the decoupling capacitance from 50uf/channel stock to 150uf/channel. This amp loves more decoupling capacitance!
It installs in the vacant hole left by the old bias supply dual section can. An additional mounting clamp is included.

(2) .1uf/630 volt polypropylene film & foil bypass caps for V1/V4 decoupling.

(1) Surge limiter kit (recommended with the larger low ESR caps)

(1) additional 100uf/100 volt Nichicon Muse KZ cap to further beef up the bias supply

(1) 6 amp fuse to replace the 8 amp stock fuse. With the limiters, the 6 amp fuse offers better protection.

(2') 18 ga. teflon wire, for the revised speaker "G" terminal grounding scheme. A big help!


Here's what he says about those resisitors:

Tip: The stock Citation II stands the cathode of the output tubes on 15 ohm resistors. If you'd like to reduce the bias current and still use the
stock bias meter setting procedure, replace the stock value with:

18 ohms for 80 to 85 ma. bias current, or

20 ohms for 70-75 ma. bias current

This assumes an approximately 465 volt plate supply. Specifications call for 450 volts on the plate, but with today's higher AC line voltages
460-470 volts is common. See the Citation Modifications Page for detailed instructions on how to do it.
 
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Could use some instructions on where to go with voltmeter,dc or ac etc,also I am positive I installed new resistors for bias 18 ohm?come up with more tonight when i get home and pics
 
maciek said:
Could use some instructions on where to go with voltmeter,dc or ac etc,also I am positive I installed new resistors for bias 18 ohm?come up with more tonight when i get home and pics
Click to expand...

Set the Voltmeter to DC. If it is autoranging, allow the meter to set its own range. If it is not autoranging set the range to 500 V for the plate and screen. For the grid and cathode, turn the range down one step at a time till you get a valid reading.

If it is a digital meter, connect the minus or common to the chassis and the hot to each of the pins in turn, noting the reading each time. The reading on the grid should produce a minus (-) sign on the left of the display.

If it is an analog meter, connect the minus or common to the chassis for the plant, screen and cathode and the positive lead to the pin on the tube. Reverse that for the grid. You will need to supply the negitive sign on the reading when you right it down in this case.

Shelly_D
 
Just came back home, gave closer look at bias ac bal switch and found out why it was not working,bias side was not connecting touching connectors,iam gonna plug it and see what it is going to do,thanks for all guidence so far,bytw meter suppose to read correct with changed resistors
 
I made meter to work,means the switch is working,still redplating on those two,i try to make measurments,
 
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