The VCXO circuitry is somewhat complex and is implemented entirely with discrete components including several semiconductors, a 15.5 MHz crystal, a varactor diode, three variable inductors, and numerous resistors and axial lead ceramic capacitors of the type that were found failed elsewhere on the RF & Analog board. I have visually inspected this circuit under a magnifier and have checked several voltages but have so far not been able to identify a reason why the VCXO is not working. Given the number of components involved and without any clear indication of a component failure, it makes no sense to me to start replacing components, some of which may be available only by salvaging from another RV75 RF & Analog board.

I'm wondering what to do with the chassis screws that are broken off in their pem (I think that's what they are called) nuts. I can't imagine the nuts are designed to be pulled out and replaced. Anyone have experience to share here, please?

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1. Match for Capacity (mFd) and Working Voltage (VDC)
2. Select for Screw Terminal Spacing?
3. Select to be No Larger than Original (Diameter, Height)

Remember this is a triode. There is roughly a 1/2 inch separation between
the inside face of the plate cylinder and the grid. There is a tiny
distance between the grid and the filament and that is where most of the
shorts develope.
So if the grid/ filament is shorted (you can measure this with an
ohmmeter) the tube is likely not salvageable. These are the ones you make
lamps out of.

Bumping the plate structure does little movement to the grid. You would
think that with a +- $300 each you would get a better deal. Too bad as
when they are good and in service barring abuse they last a good while.

David Assaf III
W5XU VP8RXU

On Tue, Feb 13, 2024, 11:52 PM Jim Shorney <jimNU0C@...> wrote:

Not even going to try with the one I found. While I don't see anything
rolling around inside the envelope, I do definitely hear mechanical noises
from inside the plate structure when the tube is rotated or gently shaken.
I would not trust it even if I could get the plate straight.

73

-Jim
NU0C

On Tue, 13 Feb 2024 22:13:54 -0600 (CST)
"Gary Follett" <xntrick1948@...> wrote:

The Eimac 3-500Z is one of the most fragile tubes in existence in terms

of the plate support structure. However, you CAN repair a bent 3-500Z by
banging it against a firm, but not hard surface just hard enough to swing
the plate back into the desired neutral centered position. I have done this
dozens of times with great results. Best to do the tapping below the
centerline of the plate relative to the base.

Gary

W0DVN

On 02/13/2024 10:31 AM CST Joe - W7RKN <w7rkn.7@...> wrote:



Sorry Jim….The courts have ruled otherwise. You are buying a specific

amount of ‘bulk’ insurance, say $500.00…that is what you are entitled to if
there is a loss. If the item shipped was valued at, say, $354.95 and you
bought insurance for $354.95, then *that* is what you would receive in a
loss.

Joe - W7RKN



From: [email protected] [mailto:[email protected]] On Behalf

Of Jim VE7RF

Sent: Tuesday, February 13, 2024 2:13 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] All bent out of shape (3-500z) - now shock

sensor value question

On Tue, Feb 13, 2024 at 01:57 AM, Joe - W7RKN wrote:

<When we purchase shipping insurance through whomever, they will

always tell you to submit an invoice for the product loss. I tell them,
nuts to you…I paid for 500 dollars of insurance, cut me a check for 500
dollars. I took UPS to court on <this a number of years ago and won. Just
an FYI!

## You can't insure it for more than it's worth.

--

73

-Jim
NU0C

The Eimac 3-500Z is one of the most fragile tubes in existence in terms of the plate support structure. However, you CAN repair a bent 3-500Z by banging it against a firm, but not hard surface just hard enough to swing the plate back into the desired neutral centered position. I have done this dozens of times with great results. Best to do the tapping below the centerline of the plate relative to the base.

Gary

W0DVN

On 02/13/2024 10:31 AM CST Joe - W7RKN <w7rkn.7@...> wrote:



Sorry Jim….The courts have ruled otherwise. You are buying a specific amount of ‘bulk’ insurance, say $500.00…that is what you are entitled to if there is a loss. If the item shipped was valued at, say, $354.95 and you bought insurance for $354.95, then *that* is what you would receive in a loss.



Joe - W7RKN



From: [email protected] [mailto:[email protected]] On Behalf Of Jim VE7RF
Sent: Tuesday, February 13, 2024 2:13 AM
To: [email protected]
Subject: Re: [DRAKE-RADIO] All bent out of shape (3-500z) - now shock sensor value question



On Tue, Feb 13, 2024 at 01:57 AM, Joe - W7RKN wrote:

<When we purchase shipping insurance through whomever, they will always tell you to submit an invoice for the product loss. I tell them, nuts to you…I paid for 500 dollars of insurance, cut me a check for 500 dollars. I took UPS to court on <this a number of years ago and won. Just an FYI!

## You can't insure it for more than it's worth.

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Progress on repairing my RV75 has come to a halt. In attempting to perform the alignment procedure in the Operator’s Manual, I have discovered that the VCXO is not oscillating. The VCXO is a voltage controlled crystal oscillator which uses a varactor diode to “pull” a 15.5 MHz crystal oscillator frequency to provide fine tuning for the PLL. Without the signal from this oscillator the PLL will not lock and stabilize the RV75 output frequency.

The VCXO circuitry is somewhat complex and is implemented entirely with discrete components including several semiconductors, a 15.5 MHz crystal, a varactor diode, three variable inductors, and numerous resistors and axial lead ceramic capacitors of the type that were found failed elsewhere on the RF & Analog board. I have visually inspected this circuit under a magnifier and have checked several voltages but have so far not been able to identify a reason why the VCXO is not working. Given the number of components involved and without any clear indication of a component failure, it makes no sense to me to start replacing components, some of which may be available only by salvaging from another RV75 RF & Analog board.

My best current idea for a fix is to send the RV75 off to someone who knows this device far better than I do; apparently wishful thinking on my part as I have been unable to identify someone who both fits this description and is willing to take on this repair. So, for now I will put the RV75 back on the shelf while I turn my attention to other projects and give some background thought to how best to proceed. This is disappointing in that this RV75 is in excellent cosmetic condition, and I have been able to verify that it is apparently working as it should otherwise.

I am still interested in purchasing RV75 repair parts, including a working RF & Analog board, VCXO crystal, VCXO variable inductors, etc. should someone on this forum have these available.

Interesting footnote: An RV75 has been listed on eBay over the last few days for an auction sale, with the auction ending last night. This unit was described as “not working, for parts or repair” and appeared to be in very rough cosmetic condition in the single photo posted. I decided to monitor the bidding on this item for the last five minutes of the auction. When I tuned in there were about seven bids, with the highest at $150. From prior experience on eBay I knew that the real bidding excitement would likely come in the last few seconds of the auction. I wasn’t disappointed. In the last three seconds, two bids were posted, one at $450, and the final bid at $477. Madness!

Rick

K8EZB

?

<When we purchase shipping insurance through whomever, they will always tell you to submit an invoice for the product loss.? I tell them, nuts to you…I paid for 500 dollars of insurance, cut me a check for 500 dollars.? I took UPS to court on <this a number of years ago and won.? Just an FYI!

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