[Amps] Amps Digest, Vol 262, Issue 17

dbritchie at gmail.com dbritchie at gmail.com
Tue Oct 29 19:20:36 EDT 2024 

Sell the 3cx400s for close to $250-300 each - post on eHam and they will evaporate quickly;
Buy new 3-500zs for about the same on eBay. 

OR

Sell the 3CX800s for $500-1000 the same way and
Buy a good Alpha 78 (Actually about 4 of them) and keep the 8874s for your great great great grandkids to use as spares.

Don't beat yourself to death redesigning 60-year old radio hardware to make it look like 40-year old radio hardware.  If the power supply burned itself up, there is a reason.
(If you still want a project, replace the Alpha plate chokes with ones non-resonant on 24MHz)

😊
David W6DR

-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of amps-request at contesting.com
Sent: Tuesday, October 29, 2024 2:56 PM
To: amps at contesting.com
Subject: Amps Digest, Vol 262, Issue 17

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Today's Topics:

   1. 3-500z substitutes (Paul Decker)
   2. Re: 3-500z substitutes (Mike McCarthy, W1NR)
   3. Re: 3-500z substitutes (Victor Rosenthal 4X6GP)
   4. Re: 3-500z substitutes (Victor Rosenthal)
   5. Re: 3-500z substitutes (Aleksandar Petkovic)


----------------------------------------------------------------------

Message: 1
Date: Tue, 29 Oct 2024 12:56:46 -0400 (EDT)
From: Paul Decker <kg7hf at comcast.net>
To: amps at contesting.com, amps-request at contesting.com
Subject: [Amps] 3-500z substitutes
Message-ID: <921267819.1276116.1730221006085 at connect.xfinity.com>
Content-Type: text/plain; charset=UTF-8

Hey gang.
I'm the proud owner of an AL-80A that's an absolute basket case. Tube is gone, HV section looks like it needs a rebuild. 

My "in stock tubes are: Qty 6 - GI-46B, Qty 6 - 3cx800A7 and U7, Qty 6 - 3cx400A7 and U7, Qty 2 -TH308, Qty 2 -TH328, Qty 2 - 8791, Qty 4 - 7213, Qty 2 - 7650, Qty 2 - 4cx1500B, (4cx350/250/150, 2c39, some other power tubes I don't really know) and sockets for all except the GI-46B and 4cx1500B.  

The goal is "fix'er up" with buying as little as possible. I'm leaning towards the GI-46B an the other triodes since there is no need for any extra screen bias voltages or control. The pair of 3cx400U7's (or 800's) would fit in real nice too, except it then requires some kind of forced air cooling mechanism. 

It looks like it's using a voltage doubler for a no load voltage of 3000V and loaded voltage of 2700V. I could pull a few windings off the transformer to lower it down a bit for the 3cx400/800 tubes, or just run at 2700. 

What do you all think would be the best fixer up route?   

Paul.



------------------------------

Message: 2
Date: Tue, 29 Oct 2024 13:53:39 -0400
From: "Mike McCarthy, W1NR" <lists at w1nr.net>
To: amps at contesting.com
Subject: Re: [Amps] 3-500z substitutes
Message-ID: <cfaae6a7-ba2f-4a1b-b600-e9611b05b14e at w1nr.net>
Content-Type: text/plain; charset=UTF-8; format=flowed

I would start by comparing the schematic and components of the AL-800 
(factory stock 3cx800A7) just to see what parts are the same and what is 
different. I am assuming they are reasonably close. Biggest difference 
would probably be filament voltage and cathode circuit.

On 10/29/2024 12:56 PM, Paul Decker via Amps wrote:
> Hey gang.
> I'm the proud owner of an AL-80A that's an absolute basket case. Tube is gone, HV section looks like it needs a rebuild.
> 
> My "in stock tubes are: Qty 6 - GI-46B, Qty 6 - 3cx800A7 and U7, Qty 6 - 3cx400A7 and U7, Qty 2 -TH308, Qty 2 -TH328, Qty 2 - 8791, Qty 4 - 7213, Qty 2 - 7650, Qty 2 - 4cx1500B, (4cx350/250/150, 2c39, some other power tubes I don't really know) and sockets for all except the GI-46B and 4cx1500B.
> 
> The goal is "fix'er up" with buying as little as possible. I'm leaning towards the GI-46B an the other triodes since there is no need for any extra screen bias voltages or control. The pair of 3cx400U7's (or 800's) would fit in real nice too, except it then requires some kind of forced air cooling mechanism.
> 
> It looks like it's using a voltage doubler for a no load voltage of 3000V and loaded voltage of 2700V. I could pull a few windings off the transformer to lower it down a bit for the 3cx400/800 tubes, or just run at 2700.
> 
> What do you all think would be the best fixer up route?
> 
> Paul.


-- 
73 de Mike, W1NR

THAT was the equation. EXISTENCE!... SURVIVAL... must cancel out... 
programming!

- Ruk -




------------------------------

Message: 3
Date: Tue, 29 Oct 2024 20:43:03 +0200
From: Victor Rosenthal 4X6GP <k2vco.vic at gmail.com>
To: amps at contesting.com
Subject: Re: [Amps] 3-500z substitutes
Message-ID: <fe7494c6-fd0f-40d1-8802-c69d815bd301 at gmail.com>
Content-Type: text/plain; charset="UTF-8"



------------------------------

Message: 4
Date: Tue, 29 Oct 2024 20:43:37 +0200
From: Victor Rosenthal <k2vco.vic at gmail.com>
To: amps at contesting.com
Subject: Re: [Amps] 3-500z substitutes
Message-ID: <25f70274-7990-400e-b7f9-85272db0e4c0 at gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

An AL80A has one 3-500Z and the transformer certainly can't handle a 
pair of 3cx400 or 800s. Also the bandswitch is a weak spot even for the 
stock setup, as is the tank coil. So unless all you are re-using is the 
chassis, it would be simplest to hunt around for another 3-500z. Maybe 
someone will trade one for one of the other tubes!

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco

On 29/10/2024 19:53, Mike McCarthy, W1NR via Amps wrote:
> I would start by comparing the schematic and components of the AL-800 
> (factory stock 3cx800A7) just to see what parts are the same and what 
> is different. I am assuming they are reasonably close. Biggest 
> difference would probably be filament voltage and cathode circuit.
>
> On 10/29/2024 12:56 PM, Paul Decker via Amps wrote:
>> Hey gang.
>> I'm the proud owner of an AL-80A that's an absolute basket case. Tube 
>> is gone, HV section looks like it needs a rebuild.
>>
>> My "in stock tubes are: Qty 6 - GI-46B, Qty 6 - 3cx800A7 and U7, Qty 
>> 6 - 3cx400A7 and U7, Qty 2 -TH308, Qty 2 -TH328, Qty 2 - 8791, Qty 4 
>> - 7213, Qty 2 - 7650, Qty 2 - 4cx1500B, (4cx350/250/150, 2c39, some 
>> other power tubes I don't really know) and sockets for all except the 
>> GI-46B and 4cx1500B.
>>
>> The goal is "fix'er up" with buying as little as possible. I'm 
>> leaning towards the GI-46B an the other triodes since there is no 
>> need for any extra screen bias voltages or control. The pair of 
>> 3cx400U7's (or 800's) would fit in real nice too, except it then 
>> requires some kind of forced air cooling mechanism.
>>
>> It looks like it's using a voltage doubler for a no load voltage of 
>> 3000V and loaded voltage of 2700V. I could pull a few windings off 
>> the transformer to lower it down a bit for the 3cx400/800 tubes, or 
>> just run at 2700.
>>
>> What do you all think would be the best fixer up route?
>>
>> Paul.
>
>



------------------------------

Message: 5
Date: Wed, 30 Oct 2024 05:56:00 +0800
From: Aleksandar Petkovic <vk6apk at bigpond.com>
To: amps at contesting.com
Subject: Re: [Amps] 3-500z substitutes
Message-ID: <b3766870-1f51-4579-b149-8e732155915c at bigpond.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

Easy. Sell some of your tubes and buy a new 3-500Z.

73, Alek VK6APK

PS: what would you want for a pair of 3CX800A7s?


On 30/10/2024 12:56 am, Paul Decker via Amps wrote:
> Hey gang.
> I'm the proud owner of an AL-80A that's an absolute basket case. Tube is gone, HV section looks like it needs a rebuild.
>
> My "in stock tubes are: Qty 6 - GI-46B, Qty 6 - 3cx800A7 and U7, Qty 6 - 3cx400A7 and U7, Qty 2 -TH308, Qty 2 -TH328, Qty 2 - 8791, Qty 4 - 7213, Qty 2 - 7650, Qty 2 - 4cx1500B, (4cx350/250/150, 2c39, some other power tubes I don't really know) and sockets for all except the GI-46B and 4cx1500B.
>
> The goal is "fix'er up" with buying as little as possible. I'm leaning towards the GI-46B an the other triodes since there is no need for any extra screen bias voltages or control. The pair of 3cx400U7's (or 800's) would fit in real nice too, except it then requires some kind of forced air cooling mechanism.
>
> It looks like it's using a voltage doubler for a no load voltage of 3000V and loaded voltage of 2700V. I could pull a few windings off the transformer to lower it down a bit for the 3cx400/800 tubes, or just run at 2700.
>
> What do you all think would be the best fixer up route?
>
> Paul.
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



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