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Author Topic: 3-500Z Tubes for Drake L-4B  (Read 4253 times)
W8RID
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Posts: 45




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« on: March 14, 2011, 06:30:49 PM »

I've had this amp for a while now. Just getting around to getting it online.

Have it all hooked up correctly. But don't seem to be getting anything out of the Amp. (no power out the back side.)(Yes, I have it going in)

I have been through a ton of trouble shooting with it. Can't seem to find anything obvous that is wrong.

I am wondering about the tubes. They glow when the unit is on. I know that does not mean that they work.

I do have 1 extra tube that has never been used and is still in its original packaging.

Is there any way I can test the tubes that are currently in the unit to see if they are. or one of them is bad?? If there is a way how do you do it??

Bob
W8RID
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W8JX
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« Reply #1 on: March 14, 2011, 06:51:40 PM »

When you apply drive does it develop grid and or plate current?
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W8RID
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Posts: 45




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« Reply #2 on: March 15, 2011, 02:36:45 AM »

Negative. I get nothing on my meters.

Bob
W8RID
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KA5N
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Posts: 4380




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« Reply #3 on: March 15, 2011, 03:53:56 AM »

Does it have high voltage?  You say the meters don't read anything.  Has it ever worked since you have owned it? You are going to have to provide more information if you expect any help.

Allen
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W9PMZ
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« Reply #4 on: March 15, 2011, 05:23:09 AM »

what is the rig that you are using?

you have the relay connected?
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VR2AX
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Posts: 577




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« Reply #5 on: March 15, 2011, 05:50:34 AM »

1. Let's try a logical step by step approach. Make sure the male HV Millen  plug from the power supply is connected to the female Millen HV connector on the back of the L-4B. Switch the meter switch on the front panel to HV - you should see a reading of around 2.5KV. What reading if any do you see? If you have no HV reading then, most likely, you have a power supply problem. If you see around 2.5kV move on.

2. Remove the transceiver coax drive cable and the keying cable from the TCVR from the amp. Insert a RCA / Phono male plug 'shorted' (ie a shorting wire between the ground and inner conductor of the plug) in the keying socket on the back of the amp. Pull the 'Standby' switch on the front left bottom side of the amp outwards. You should see around 200mA of plate current indicated, this is idle current. No grid current will be indicated. What reading if any do you see? If you don't see any, you might have bad tubes, but you might also have a problem with the TX/RX change over relay, or the 24V DC supply that powers the relay, or simply a bad connection somewhere in the relay line.

3. If you see "0" plate current indicated when you carry out step 2, do you nevertheless hear a noticeable audio "click" or "clunk" when you pull out the Standby switch (with the shorted RCA plug in place)?

Let us know how you get on. Like Allen said less info is less than more which is needed here.

Wyn

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W9PMZ
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« Reply #6 on: March 15, 2011, 06:47:27 AM »

if there is no clunk from the relay then there is no grid current etc.

this is why the relay should be looked at first.

if you are using a "modern rig" and the amp relay circuit you could have blown it with the 120v relay control on the L-4B
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W8JX
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« Reply #7 on: March 15, 2011, 07:37:15 AM »

Need to check for plate voltage too. Make sure B plus it there and then check on relay.
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VR2AX
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« Reply #8 on: March 15, 2011, 07:59:24 AM »

Quote
if you are using a "modern rig" and the amp relay circuit you could have blown it with the 120v relay control on the L-4B

It is 24V V DC line. Current may be high for a modern solid state radio.
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W8JX
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« Reply #9 on: March 15, 2011, 08:02:50 AM »

It is 24V V DC line. Current may be high for a modern solid state radio.

The L4B was built like a tank and I have little doubt that relay control current demands would overload most newer SS rigs meaning if amp has B plus and not keying and it is wired correctly then relay is fried in exciter. 
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WB2WIK
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« Reply #10 on: March 15, 2011, 09:01:03 AM »

Negative. I get nothing on my meters.

Bob
W8RID

That wouldn't be a tube problem.

Something's not connected, or the T-R relay in the amplifier is not keying.
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W8JX
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« Reply #11 on: March 15, 2011, 09:58:56 AM »

Negative. I get nothing on my meters.

Bob
W8RID

That wouldn't be a tube problem.

Something's not connected, or the T-R relay in the amplifier is not keying.

But it would still show plate voltage regardless or T/R rely operation.
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KA5N
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« Reply #12 on: March 15, 2011, 01:07:32 PM »

I know this sounds stupid, but did you plug it in?  If so is it wired for the correct AC voltage?
Are the fuses blown?  Is the power switch good?  Do the tubes light up?  Have you read both
the manual for your transceiver and the manual for the amplifier?
Do you know a ham friend that can give you first hand assistance?

Allen
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KG6YV
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Posts: 505




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« Reply #13 on: March 15, 2011, 04:13:00 PM »

When you apply drive power do you have the potentiometer/switch in the lower left of the front panel pulled out?
The push/pull switch is for switching the linear.  If it is "IN" the linear is bypassed "OUT" the exciter keys the amplifier.

Greg
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W8RID
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Posts: 45




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« Reply #14 on: March 23, 2011, 10:21:48 AM »

To everyone that sent a reply on something to check, Thanks!!

It took me a week to get through all the suggestions. Still not operating.

I was able to get a Drake repair person to come here and take a look at it and he said there was definately something wrong and he needed to take it to his shop and check it out more thoughouly. So that is where this issue is at right now. Waiting to hear back from him.

But, one of my original questions did not get answered.
Is there a way to check the 3-500Z tubes to see if one or both is bad??

Bob
W8RID
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