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 Post subject: Radiola 20 tube substututions
PostPosted: Nov Mon 22, 2010 8:09 pm 
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This is the second time I am writing this. Hopefully, sometime I will learn. I wrote it, clicked the preview button, decided on a small change, clicked the back button, and went back to ........ oblivion, anyway it was gone. I've done that about 3 different times. Guess I'm a slow learner. Back to the subject. I went to a radio auction the other day and among other things, I brought home a beautiful Radiola 20. The radio appears complete except that it has no tubes. Also it was marked "condition unknown" which generally means it doesn't work but that is an issue for a later date. I would of course, like to make the radio work but what I'm wondering at the moment, since 199's and 120's are so scarce and expensive, is if anyone has had any sucess at making adapters and substituting other tubes in the Radiola 20. I know that 1A5's have been sucessfully used in Radiola III's and proximity fuse peanut tubes have been substituted for 01A's but I've never seen anything that appied to a Radiola 20. I wonder if the fact that it's a neutralized TRF with a regenerative detector might complicate matters(maybe due to interelectrode capacitance). I would sure like to see some discussion on this and your thoughts and ideas will sure be appreciated.
Thanks, Robert

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PostPosted: Nov Mon 22, 2010 8:24 pm 
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Hello Robert,
I have had similar problems with dissapearing paragraphs because of some stupid time out. I have been moved to create the post in Word off line. Then I do a cntl c copy and enter it into the ARF post with a cntl v.

As to 199 availability. It may be good to have at least one set in stock if you enjoy these battery radios. Type 30 tubes are relatively close if I remember correctly...and are usually alot less money. However, they do not look right!

Seems like there is another tube (864?) that folks would also sub.

May need to look at tube manual to see what changes may be needed by using other tube types...
Eric

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 Post subject:
PostPosted: Nov Mon 22, 2010 9:02 pm 
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Edit - didn't read the previous post properly :oops:


Last edited by golfguru on Nov Tue 23, 2010 1:22 am, edited 1 time in total.

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 Post subject:
PostPosted: Nov Mon 22, 2010 10:45 pm 
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The Radiola 20 uses ux-199's and a ux-120 for an output tube. No modifications or bulletins were ever issued to convert tube types for the Radiola 20. The '99 & 120 both have a 3.3volt filament rating, the rheostats, neutralizing, grid leak and regeneration are all based on this tube type.

Both '99's and 120's are available from a variety of vendors and individuals. Keep in mind that low emission 99's can be rejeuvenated.

There is a tubular type 30 that may work if the filament source is 2.2volts.

Note too, that -22-1/2 is need for the output stage.

Ring out the audio transformers, they are the same 3:1 as used in the Radiola III.

Place a classified for the tubes you need...

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 Post subject:
PostPosted: Nov Tue 23, 2010 7:55 am 
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What is the filament current of a UX-199 and a UX-200 anyhow?
Best Regards
Arran


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 Post subject:
PostPosted: Nov Tue 23, 2010 5:01 pm 
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My RCA R-10 manual says the filament voltage and current for a UX-120 is 3.0/3.3 V and the current is 0.125/0.132 A. The corresponding values for a UX199 are given as 3.0/3.3 V and 0.060/0.063 A.

I have read of subminiature type 5676 tubes being substituted for '99's with apparently excellent results, the current being adjusted with resistors. I don't know if the slight difference in grid-plate capacitance might cause a problem witn this application because of neutralization. 5676's seem to be fairly easy to find and are relatively inexpensive.

I have not seen anything on substitutions for the output tube, the UX120. I'm wondering if it might be possible to use Two 5676's in paralell with filament in series. This could all be mounted on a plug-in adapter.

I agree, I need to come up with one set of '99' and a 120 (maybe dud's) for display but I would like to come up with someting for everyday use that I wouldn't need to worry about.

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 Post subject:
PostPosted: Nov Wed 24, 2010 1:55 am 
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You can use 30 tubes, with a 31 for the output, I checked my set and they clear the lid. Tubular 30 are hard to locate than regular 99. Good luck with your project.


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 Post subject:
PostPosted: Nov Tue 30, 2010 5:47 pm 
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Thanks guys! I appreciate your ideas. Does anyone have any comments on the use of subminature tubes such as the 5676 for a 199? Or any idea of what subminature or acorn tube or even an octal GT, that could be used for a 120? Ken Owens, Alan Douglas, Norm Leal, are you out there? Any furthur comments?

Thanks, Robert

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PostPosted: Nov Tue 30, 2010 6:30 pm 
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This is a good place to mention one of my favorite topics which is “The C Battery”.

It seems a lot of the battery Radiolas have failed audio transformers.

Most of these take several “C” batteries. I used to shortcut the C battery until I fried a nice horn speaker from too much plate current on an 01 (Not 01A) in an RADA audio final. Noting RCA had a C battery modification for the RADA.

Now I am religious about using the Proper C battery. Some of the worst sets for transformers are the Radiola III and III-A although there are plenty of other RCA as well as other makers that have high audio transformer failure problems.

Jim


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 Post subject:
PostPosted: Nov Tue 30, 2010 8:16 pm 
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Robert

The best tubes to use would be 30 for 99's and 31 for 120. All that has to be done is reduce filament to 2 volts. A 99 and 120 are rated 3.3 volts 99 draws 60 ma and 120 - 120 ma. (These will be listed sligfhtly different in some books.)

The 30 filament draws 60 ma at 2 volts and 31 draws 120 ma at 2 volts. Using 30's & 31 look good in the radio.

5676 and similar tubes will work as a 99 with reduced filament voltage. It could also be used for 120 but has higher gain and lower drive current. It would be like using a 30 or 99 in place of 120.

What do you have to work with?

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 Post subject:
PostPosted: Nov Tue 30, 2010 10:41 pm 
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You could get along without a 120 if you didn't ned to drive a speaker too hard.

I would use a 99 in the RF stage at least, and preferably in the detector too, but the rest of the tubes could be almost anything with three electrodes.


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 Post subject:
PostPosted: Nov Tue 30, 2010 10:57 pm 
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Chas and VicJ had also mentioned using 30's and a 31 for output which sure might be the way to go. I had not considered that. 30's and 31's are not easy to find but are probably easier to find and less expensive than '99's and a 120, and obviously would look a lot better than 5676's. I'm still wondering though, if it would be feasable to use a pair of 5676's in paralell for output. Wouldn't that halve the single tubes output impeadance and approximate the output of a 120?

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 Post subject:
PostPosted: Nov Tue 30, 2010 11:11 pm 
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Robert

Like Alan mentioned don't have to use a 120 but it will limit speaker drive.

Not much gained with 2 - 5676's in parallel.

If you have 5676's wire some in 4 pin tube bases. At least this will get your radio operating.. You could cover them with 1" test tubes silvered inside. They will look almost like original 99's.

Do you have any other tubes? Any 30's, 1H4's? 1H4 is like a 30 but with octal base. It would require an adapter or rebasing.

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 Post subject:
PostPosted: Dec Wed 01, 2010 12:10 am 
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Well, I just took stock in a cold garage and layed hands on two 99's with open filaments, 3 99's with good filaments, a good 30, a good 1H4G, and 4 5676's that I bought several years ago. I guess my quickest route to getting this radio going is to fill out with 99's if you think the 99 will drive a UZ 1325 horn. At least I'll have something that will look good. I can experiment with the 5676's after I get the radio going.

Thanks again, Robert

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 Post subject:
PostPosted: Dec Wed 01, 2010 12:26 am 
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Robert

99's will do it. Be sure they are X99 and not V99. V99 has shorter pins and is based differently.

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 Post subject:
PostPosted: Dec Wed 01, 2010 1:18 am 
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At one time I was trying to collect the entire Radiola series and I had a Radiola 20 on my shelf.

I was up in the attic of a ladies house and spotted a little table stuffed down in a pile of stuff that had the design of the Radiola 20 panel engraved in a drawer but without the two tone effect; and the top of the table was about the size of the base of the 20.

After I pled my case and got it home and dusted it off and stationed the Radiola 20 on top, there was a compartment in the back of the table that held the dry cell batteries with a door that snapped in place and a card stapled to the door that explained how to install and connect the batteries.

I always wondered how many of these early sets could have had matching furniture.

I never managed to gather enough batteries to keep some of these sets in operation.

Jim


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 Post subject: Re: Radiola 20 tube substututions
PostPosted: Dec Wed 01, 2010 1:40 am 
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rbstul wrote:
This is the second time I am writing this. Hopefully, sometime I will learn. I wrote it, clicked the preview button, decided on a small change, clicked the back button, and went back to ........ oblivion, anyway it was gone. I've done that about 3 different times.

There's no reason to hit the Back button, just scroll down the page. The open Edit window is just below the Preview on the same page.

Larry

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 Post subject:
PostPosted: Dec Wed 01, 2010 1:41 am 
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That's pretty neat. I never saw a Radiola 20 with a matching table or stand but I do have a Radiola 60 with an aftermarket stand and a Westinghouse WR-10A table model in an aftermarket cabinite that makes a lowboy out of it.

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 Post subject:
PostPosted: Dec Wed 01, 2010 1:43 am 
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Yeah, thanks Larry, as I said I'm a slow learner.

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