[Amps] 3-500z substitutes

[Victor Rosenthal]

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.
>
>