harman kardon citation ii

[bktheking]

I always test with tubes in, but that's me. You'll see the voltage when it starts to red plate, then shut it down.

 

[maciek]

First time measured on live circuit,radio shack analog meter,v7 3- 250v,4-220v,5-150v going to250v,8-48to50v that's the one redplating,now v8 that's going nice and I was able to bias with fixed switch and working meter:3-225v,4-225v,5- needle went to the left negative I assume cant tell the number thou,8-25v,did not do any more casue am exhausted, need to get better meter and will do exact try to post some pics

 

[maciek]

pics

some pictures

 

[bktheking]

Those numbers are really low, I haven't worked on a citation but my st-70 pin 3 and 4 were up around 440Volts.

 

[Westy56]

The solder looks sparsely applied to the ac balance pot.
Have you re checked all your connections?

Steve

 

[shelly_d]

...

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

First time measured on live circuit,radio shack analog meter,v7 3- 250v,4-220v,5-150v going to250v,8-48to50v that's the one redplating,now v8 that's going nice and I was able to bias with fixed switch and working meter:3-225v,4-225v,5- needle went to the left negative I assume cant tell the number thou,8-25v,did not do any more casue am exhausted, need to get better meter and will do exact try to post some pics

With an analog meter, you must reverse the test leads to get the reading on pin5 - the grid.

You have found the cause of your redplating. Pin 5, the grid must be a negative voltage to reduce the current flow through the tubes. It is VERY positive. You must now find the reason for that high voltage.

With the amp unplugged, trace the wiring of the amp, from pin 5 back to the power supply components of the bad channel, comparing it to the good channel step by step. Make sure the two channels are identical. I am assuming that they will not be. Be very careful doing this because, as I recall the circuit, there is a lot of switching in the amp, some if it may be in the bias circuit. If you need to, use your meter to test continuity (ohms) through the switching for both channels.

MAKE SURE THE AMP IS UNPLUGGED AND THE POWER SUPPLY CAPS ARE DISCHARGED BEFORE DOING THIS.

 

[maciek]

Thanks Shelly for guidance,that's great now I know what to look for could be that have wrong resistors installed letting higher voltage to pass to tubes?cheers

 

[shelly_d]

Thanks Shelly for guidance,that's great now I know what to look for could be that have wrong resistors installed letting higher voltage to pass to tubes?cheers

I don't think the wrong resistor is the issue here. Your amp has a section of the power supply that produces a negative DC voltage. It feed that voltage through a bias adjustment and on to the grid pin of the output tubes. To keep that voltage correct, there are coupling capacitors that separate the grids of the output tubes from the outputs (plates) of the phase splitter tubes which are a high positive voltage.

There are a number of things that could go wrong that could cause the high positive voltage on the grid of the output tubes. You need to be very methodical about tracing this down. The first is the make absolutely sure that the circuit that supplies the negative voltage is doing what it should do and is properly connected to the grid terminals of the output tubes.

Shelly_D

 

[shelly_d]

I have just looked at the circuit for the amp. You have 4 bias pots, one for each tube. One end of each pot is ground, the other end of each is tied to the bias supply. You can use this to your advantage.

Turn off the amp, remove the tubes and allow time for the caps to discharge. Open it up and remove the bottom. Identify the bias pots feeding the good channel and the pots feeding the bad one. You should be able to identify the ground terminal of each pot. The other end of each pot is all tied together back at the bias supply. With all the caps discharged, you can use your multimeter on resistance to measure the resistance between the top of the bias pots of the good channel to the top of the pots of the bad ones. You should see 0 ohms. I'm betting that you will see a large resistance or even open. If so, that will prove that the bad channel is disconnected from the supply.


Remember: The caps must be discharged to prevent shock and damage to your meter.

 

[maciek]

Did not get to check it yet ,need to find my discharging tool,would it mean that those two bias pots are bad or disconeccted,could they use deoxit?remember when before all that upgrading work, bias pots dont remember exactly which would make the meter flicker like crazy,now bad ones dont move,just to mention this citation ii is one of the first models with big ass meter and no vent holes on top of chassis,might be 60 yeras old,cheers

 

[shelly_d]

Did not get to check it yet ,need to find my discharging tool,would it mean that those two bias pots are bad or disconeccted,could they use deoxit?remember when before all that upgrading work, bias pots dont remember exactly which would make the meter flicker like crazy,now bad ones dont move,just to mention this citation ii is one of the first models with big ass meter and no vent holes on top of chassis,might be 60 yeras old,cheers

Just take it one step at a time. Find out if the bias pots are properly connected or not.

If the test shows that all the bias pots are properly connected then make sure that the wiper lead is connected to the input side. I think this is less likely since there are separate pots for each tube. Most likely there is one problem that is causing the red plating. I think you mentioned that both tubes are red plating. That suggests to me a problem that is common to both tubes.

Shelly_D

 

[maciek]

few pics of bias pots

pics of bias pots and rear

 

[maciek]

One thing makes me wonder,it played with no issues after coupling caps replacement,only work i did around bias pots was replacing resistors,that is good question it is something affecting just those two tubes

 

[shelly_d]

Then very carefully check each of those connections. There is a resistor from the bottom of the bias pots to ground. Was that part of the change? An open in that part of the circuit could cause the problems you are having. If there is no open, then are both channels equipped with the same value resistor and are they in spec?

Could your work on it cause a break in the bias circuit?

Go back over the bias circuit from start to finish to find the issue.

Shelly_D

 

[maciek]

It is going to take while to go through all this going to let you know if I found something I did some soldering on bias ac balance switch maybe there are bad solder joints

 

[PakProtector]

hey-Hey!!!,
With one pair working there must be a functioning bias supply( generating filtered negative voltage ). On the functional side pull a power tube and measure resistance between pin 5 at the socket from the top to ground. Should be the value of that grid resistor( 100kOhms ) plus part of the bias pot. This will also change when you adjust the bias pot. Repeat for the bad side.
cheers,
Douglas

 

[maciek]

Re

Heyhey it is not that one channel is bad and another good,each channel has one tubegood and one redplating,that bad are v7 and v9,could this be bad bias pots,also start wondering if bias supply is wired correctly,that came with Jim mcShane kit,but picture was blurry copy so I followed instructions on building it from tubesRit.com,can anyone tell if it is correct,thre are to caps,resistor and diode,or maybe picture or drawing of it thanks

 

[maciek]

Hi Shelly

Wanna thank again for your help Shelly,after awhile I found two resistors coming from pin 5 tied to wrong turrets 14 not 15,this was causing redplating,thanks again

 

[shelly_d]

Wanna thank again for your help Shelly,after awhile I found two resistors coming from pin 5 tied to wrong turrets 14 not 15,this was causing redplating,thanks again

Glad you found it. The Citation II is too nice an amp to give up on.

Shelly_D

 

[maciek]

re

Time passed by and listening to upgraded hk cit ii makes me think it sounds kinda dry and thin,sometimes i think my eico hf-87 sounds better ,just wondering if either needs improvement