Worldwide DX Amateur Radio Forums - Ham - CB - HF - VHF - UHF

I thought I would move this thread to the Home Brew section and make it sticky so it will be easier to follow the progress. I will also start my own and drop some pix as time goes by.

__________________
Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

Sounds great!
Did not get off work until late today. In fact just got home 30 minutes ago. Had to cover for someone. So probably want get nothing done here.

QRN do you have a 572B handy? If so measure from the top to the tube base so I can see if I have the clearance I need when so if I switch to that tube. I do not have one at the moment.

Sorry no 572B's on hand, just some 811A's. Check this link out for the original specs of the 572B,both physical and electrical specs.

http://www.r-type.org/pdfs/572b.pdf

__________________
Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

Russian tubes.

I like em. They are cheap (we will come back to this), has reasonable filament demands and make good power.

Downsides:

1) These tubes are RUSSIAN SURPLUS. You need to understand that when the surplus dries up, thats it. The price will go through the roof, no one will rebuild them and you will be left with an amp that is about as useful as a 12 tube Phantom with 6lQ6's. These are the cheap and plentiful sweep tubes of today. If someone was to do a 35b box I would buy all my spares now while I could and sit on them. I have already seen the price tag jump over the last 4 years. First they were $85, now they are like $120 or so last time I looked.

2) They are not a zero bias triode and require quite a bit of biasing to prevent them from running wild and drawing too much current at idle. they can draw almost .4 amp each at idle in grounded grid with no bias applied.
in contrast a 3cx3000a7 will draw anywhere from .230-.4 at idle BUT has a mush higher total output and plate dissipation.

3) All the data sheets I have seen for the 35b tend to have different info. , all different values etc etc. this bothers me. I think this is why when testing these tubes I find one can draw a considerable amount more current than the one next to it(filament)

4) only one guy makes a socket and chimney and its expensive. I have seen some good homebrew solutions though.

__________________
Bomb Diggity!
_____________________________________
Quote Bob85: "peoples' personal non factual opinions mean nothing to me period, BS is 10 cents a gallon anywhere you look for it"

Thanks for the Russian tube info linearone.
I myself have not done much with them but have been doing a lot of reading up. I do have a couple I am going to do a tube swap in a MLA 2500. Just waiting to get rest of the parts.

Thanks for the link QRN. That was helpful.

This morning I finished tearing the chassis down and got it all sanded. Next is to get the RF deck fabricated. The tube compartment will drop 1 inch lower than the top of the chassis. This way I can make a full enclosure for the tube compartment and have good shielding. I also will blow air up and across the tubes. This way we should be able to get the heat out of the box instead of blowing across other components.

More to come.

I have been asked a lot of times why I don't go with the Russian tubes and the simple answer is that I don't want to use any type of ceramic tube. I simply prefer glass tubes. The big amp I plan to make will have a certain vintage look to it and ceramic tubes were simply not around in that era. Both it and especially the 572B project will be used as part of a classic AM station and ceramic tubes just don't fit in from a continuity point of view. The 811A and 572B have been around for 50-60 years and fit in nicely. Besides, the soft glow of the filaments behind a glass panel or as seen thru a screened RF deck is eye candy to some of us. There is nothing wrong with using ceramic tubes mind you, it's just that in some cases nostalgia takes precedence. Running a Heath DX-60 or Viking 2 into a 3CX1500 just ain't right IMHO.

__________________
Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

without a doubt I think glass tubes are prettier too. I love to see the glow.

but, there sure is something sexy about a 3cx15000... maybe its the handles....

__________________
Bomb Diggity!
_____________________________________
Quote Bob85: "peoples' personal non factual opinions mean nothing to me period, BS is 10 cents a gallon anywhere you look for it"

I love the power of the ceramic's but there is just something about te glow of those tubes on a cold winter day in the shack.

Ok, back to the amp build.

I fabricated a piece of metal for the tubes to sit on. About an inch below the to of the chassis. This was then spot welded into the main chassis and the top was cut out. Now I can sand, file and paint.

Now you can go out and have all this made professionally. But I like to make or use what I have available. One reason I am using this chassis that was made in 1962 (nostalgia). This is homebrew!

RF Deck installed


Top cut out for RF Deck.


Just to get an idea of how the tubes fit.

The Chinese 57b's are 6 1/8 inch from the top of the socket to the top of the anode. The Dentrons are about 1/4 inch shorter.
Rich

Last project for today.
The shield