250TH Options

[WX1WX]

While I while away the hours working on some other restorations and before I get to a new-to-me BC-610-F, I was wondering if any of you could advise me on:

The 250TH in the PA of the BC-610; If you where to decide to work around to as close to as a direct replacement as you could with the least mods... what would you go for?


de WX1WX
WX1WX@yahoo.com

[KL7OF]

I am wondering why you would want to work around the 250TH...?? The easiest way around it would be with another triode that the bc 610 power supply would handle and one that would present a close enough match so the 100TH modulator iron would be happy...I have found the 250TH to be a tough tube...I have been beating up on a pair for quite a few years now and they are still going strong..I usually run them just a little redder than red.....
   I wonder how a 3-500 would work?   Good luck and let us know what you decide....Steve

[W7TFO]

Good 250-TH tubes show up on eBay all the time.

I've amassed several for projects that way.

Make sure to over-insure and school the seller on the proper way to pack them.

4 out of 5 make it OK, no loss on the others.

73DG

[WX1WX]

What are some suggestion on packing, beside a bunch o' bubble pack?
I am looking at one in the spring and frame holder.
I'll take all the advise I can get!

de WX1WX

[WD5JKO]

  I don't think there are many direct replacements that would have good availability today. One possibility with some changes would be the 152TH, or perhaps the 304TH with one set of filaments turned off. These would boost the filament demand from 10.5 amps to 12.5 amps at 5V. The stock filament transformer might be OK. These tubes would drive easier, but the increased plate - grid capacitance would require neutralizing adjustment. Looks like a socket change too.

http://www.shinjo.info/frank/sheets/088/2/250TH.pdf
http://scottbecker.net/tube/sheets/088/1/152TH.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/088/3/304TH.pdf

Jim
Wd5JKO
   

[w1vtp]

Try networking for a 250th.  This guy got an old BC-610 and had it restored.  Nice result and good tips

http://home.comcast.net/~rbethman/BC-610.html

GL  Al

[W7TFO]

In all the shipping done to get big tubes to me, none have ever arrived 'broken'.  That is, with the outer glass envelope destroyed.

What happens is a sudden stop whilst in motion causes inertia to overstress the internal structure, causing at the very least filament failure, and most times complete dislodgement of the plate.

It must be packed to withstand a fall of at least 6 feet onto a concrete floor.

To wit, the tube (best in the original carton, spring frames don't do any good) gets boxed in a slightly larger box with ghost turds (foam peanuts for the unimaginative), then packed LIGHTLY but fully in at least a 20" cube box.  A 24" cube is much better by experience.

Insure for $500, and it might be given better treatment.  UPS and FedEx have ruined more tubes than the PO for me, and Priority Mail is quicker than Parcel Rate thereby giving them less chance to bang it around.

So far, 851's, 849's, 204A's, 450TH/TL's, 6C21's, 250TH's, 211's, 872's, 862's, HF200's, HF300's and a lot more have made the trek to the Arizona desert so I will have things to play with in the future.

A side note: Tubes with pure tungsten filaments are really tough if not used.  If they have a few hours in the socket, the filament wires have all the resilience of pencil lead.  Thoriated filaments are pretty tough all their lives.

73DG

[WX1WX]

Thanks everyone for these great ideas. I am hoping I will never have to face the day when I cannot get a 250TH, but you never know…

cheers and 73-

de WX1WX

[W2VW]

I have retrofitted both a 3-500Z and an 833A into a BC-610F.

Someone may have video of the Last Gaithersburg AM Special Event Station which used the 833 BC-610F for the main tx.

Neither are difficult. Neutralization cap needs size change and fil requirements.

Some air is needed on both especially filament pins on the 3-500.

Either will take a full gallon input if you move to Canada.

[W3GMS]

Thanks everyone for these great ideas. I am hoping I will never have to face the day when I cannot get a 250TH, but you never know…

cheers and 73-

de WX1WX

Not my handy-work, but an almost completed pair of 250TH's in push pull.  Great tubes in PP service.

Joe, GMS 

[WX1WX]

Gorgeous work!!