All tubes red plating

[kevinkr]

Confirmed here too..

[Osvaldo de Banfield]

Originally Posted by Frank Berry

A schematic would certainly help.
It sounds like this is some kind of linear amplifier. If it's a linear, it's not class C.

Sometimes the term "linear" is misunderstood. A power amplifier for FM can be class C, and also called "linear" when in true it isn´t.

[Frank Berry]

I found the schematic and published specs.
This is an 11 meter linear amplifier. Suitable for AM, SSB, FM.
Looks like it might operate in class AB mode.
Illegal in the United States.

[artosalo]

This link works:

http://www.google.fi/url?q=http://ww...XzoF_ZJxwiVyPQ

[HollowState]

The PDF can be accessed by goint to www.rmitaly.com then >download >download manuals >KLV1000-manual_rel_210.pdf

[artosalo]

According to manual the original tubes are PL509 having 40 V heater voltage, which is also used to generate the bias voltage.

Now it seems that tubes have been changed to 6P45S, which has 6,3 V heater voltage. So what has happened to bias voltage, which should be much more than just rectified 6,3 VAC can form.

The simple fact is that if tubes are redplating they are dissipating too much power/heat. This reguires high quiescent current which in turn can take place if the bias voltage is too low.

[Osvaldo de Banfield]

Artosalo: You are right. It is a biamp (RX and TX), and the values of bias are too low. He must add a 48V trafo and rewire the bias supply.

[loopy]

Originally Posted by Osvaldo de Banfield

Artosalo: You are right. It is a biamp (RX and TX), and the values of bias are too low. He must add a 48V trafo and rewire the bias supply.

Thanks for the responses. I understand about the bias voltage being too low, so I removed one end of the diode(s) and applied the 40 volts AC direct (leaving the 6.3 volts AC intact for the heater), which read about 50 volts DC on the other end of the diode, for the bias.

The same thing still occurs. I can turn the drive right down to the point where there is very little output, and they all still red plate. They take a little longer to do so, but it still happens.

[Osvaldo de Banfield]

Does the driver also gets hot plates?. May be that the problem is a VHF self oscillation, at a frequency where the plate circuit can´t absorb it. Make an easy RF power meter: a Hertz ring. Take a small incandescent lamp, the less power as possible will result in a higher sensitivity. Make a wire loop of about 50 mm (2"), (1 turn coil) and solder both ends to each pin of the lamp. Carefully, put the loop near the output LC tank, and see if with no input, the lamp brights. If this is the case, try to re-neutralize all set. Search in the web how to neutralize it, or post me and I try to explain it. It´s easy.

Also, tell me if the trouble started from a tube replacement. It points to a neutralizing trouble.

[loopy]

Originally Posted by Osvaldo de Banfield

Does the driver also gets hot plates?. May be that the problem is a VHF self oscillation, at a frequency where the plate circuit can´t absorb it. Make an easy RF power meter: a Hertz ring. Take a small incandescent lamp, the less power as possible will result in a higher sensitivity. Make a wire loop of about 50 mm (2"), (1 turn coil) and solder both ends to each pin of the lamp. Carefully, put the loop near the output LC tank, and see if with no input, the lamp brights. If this is the case, try to re-neutralize all set. Search in the web how to neutralize it, or post me and I try to explain it. It´s easy.

Also, tell me if the trouble started from a tube replacement. It points to a neutralizing trouble.

Yes. I just noticed today that the driver also gets hot plates. Another thing I've noticed is the output is always slowly rising. Say for example with about 3 watts in I get about 300 out, after about 30 seconds or so that might rise to ~350, and keep rising.

I'm not sure if I've always had this trouble, as I was unaware of red plating until the first time I had seen it a while ago. I have several of these tubes and they all respond the same way.

I don't think I have a low voltage incandescent lamp on hand, but if neutralizing is an easy task, I can try that if you can explain.

Thanks.