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HF homebrew tube amp photo build

linearone said:
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.
Click to expand...


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. :p: 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. :D
 
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
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Top cut out for RF Deck.
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Just to get an idea of how the tubes fit.
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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
 
Looks like you are off to a good start. I am working nights tonight and tomorrow night with Sunday off (sleep day) and then back to work on Monday and Tuesday :headbang which is off my normal shift rotation but it enabled me to get nine days off in a row :w00t: so I hope to get a few things started myself. I need to get some things done around the yard and put up an antenna but hopefully I can get some chassis work done. I have an old cabinet that was originally a frequency meter I think. It's about 17w X 9½h X 12d and needs a couple holes filled,sanded and a fresh coat of paint. The front panel has rack handles and will actually bolt to the homemade chassis allowing the entire innerds to be slid out for ease of service. I'll get some pix up early next week after I get a chance to tell night from day. :D On a side note,I just found out my planned 2000pf loading capacitor is about ½ inch too long to fit. :oops: Time to hit the junque box. I prefer to spell it "junque" and not "junk" because it is a higher class of junk. :whistle:
 
Hey I love junque!

Know what you mean about the night shift. Did that for 4 years. Been back on days for a little over 2 years now.

Cant wait to see you get started on yours. But I know how times is.

Paint
Going to paint the chassis with Walmart special. The paint is made by Rustoleum. It is called "Hammered" and leaves a great looking finish. They have it in many colors.
You you paint the inside of the tube compartment, (and I suggest you do) paint it with a flat color. This will keep the filaments from reflecting off the tube compartment and creating more heat. With 3-500's this is a must.


Transformer.
I am going through transformers to see what I can use. I have to look closer and see what the 811A and 572B likes. One transformer I have came from a Pride DX300. I believe this is 2000 volts after filter and rectifying.
 
QRN said:
Looks like you are off to a good start. I am working nights tonight and tomorrow night with Sunday off (sleep day) and then back to work on Monday and Tuesday :headbang which is off my normal shift rotation but it enabled me to get nine days off in a row :w00t: so I hope to get a few things started myself. I need to get some things done around the yard and put up an antenna but hopefully I can get some chassis work done. I have an old cabinet that was originally a frequency meter I think. It's about 17w X 9½h X 12d and needs a couple holes filled,sanded and a fresh coat of paint. The front panel has rack handles and will actually bolt to the homemade chassis allowing the entire innerds to be slid out for ease of service. I'll get some pix up early next week after I get a chance to tell night from day. :D On a side note,I just found out my planned 2000pf loading capacitor is about ½ inch too long to fit. :oops: Time to hit the junque box. I prefer to spell it "junque" and not "junk" because it is a higher class of junk. :whistle:
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why not just un do it and shorten it? it can be done kinda easy if you are careful. it takes loads of time though
 
linearone said:
why not just un do it and shorten it? it can be done kinda easy if you are careful. it takes loads of time though
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I thought of that but this one is a tough one. It has ceramic insulators running the length of it.It's actually two 1000pF caps laid end to end on a common frame.It would involve cutting two pieces of ceramic as well as three brass rods that run the length of it. I'll post some pix in a couple days,after the night shifts end and you will see what I mean.
 
Radio Tech said:
Paint
Going to paint the chassis with Walmart special. The paint is made by Rustoleum. It is called "Hammered" and leaves a great looking finish. They have it in many colors.
You you paint the inside of the tube compartment, (and I suggest you do) paint it with a flat color. This will keep the filaments from reflecting off the tube compartment and creating more heat. With 3-500's this is a must.
Click to expand...


GREAT! Now you are going to make me look like a copycat! I must state that I have already painted the large 42 inch cabinet for the 3-500 amp with Walmart Hammertone black and will be doing the same on the 572B cabinet. :love: BTW, a good paint for the inside is also available from Wally Mart.I used, and will be again, their "textured" black paint for outdoor metal furniture. It is flat black with a somewhat rough finish which is rougher than just a flat paint but not pebbled like that rocky texture stuff. I figure my amp will be hammertone black on the outside,textured flat black on the inside and the front panel will probably be gray hammertone or another shade of gray.I have a couple to choose from.
 
QRN said:
GREAT! Now you are going to make me look like a copycat! I must state that I have already painted the large 42 inch cabinet for the 3-500 amp with Walmart Hammertone black and will be doing the same on the 572B cabinet. :love: BTW, a good paint for the inside is also available from Wally Mart.I used, and will be again, their "textured" black paint for outdoor metal furniture. It is flat black with a somewhat rough finish which is rougher than just a flat paint but not pebbled like that rocky texture stuff. I figure my amp will be hammertone black on the outside,textured flat black on the inside and the front panel will probably be gray hammertone or another shade of gray.I have a couple to choose from.
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Well you know what they say, great minds think alike :D
I love those Wal-Mart paints. Great for covering lousy prep work like grind marks and so on. Plus gives the finish character!
 
QRN said:
That's exactlythe reason I chose the hammertone paint, to hide all the little imperfections. (y)
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That stuff works wonders and goes on al my restorations :)



Ok, The circuit.
If anyone wants to see a what this amplifier circuit looks like, this one will be close as you can get.
http://jlandrigan.com/files/DX-811A GG Linear Amplifier.pdf

This was in CQ Magazine September 1982.
Although it will differ to some extent.

I been going through transformers today.
Not having much luck. One transfomer I have came out of a Pride DX300. By the time this is rectified and filtered it will be around 2400 volts. Now that may be a proble for the 811A tubes! But this is with no load.
The 811A as I have read likes about 15 to 17 hundred volts. The transfomer under load should drop to 1800 volts @ 500ma (If I done my math right).117VAC @ 10 amps gives 1800VAC out.

Two disavantages are no CT on the secondary and no 240 input on primary.
So with 120VAC in, voltage drop across the supply, and the ground of the bridge recitifier on the TX relay, no voltage present in the stand-by mode.

I have to think about this more.
 

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