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Sub a 5AS4A for a 5U4G OK ?

#3
My 'Tube Substitution Handbook' (tenth edition), says you can use a 5AS4A to replace a 5U4G. If you need more, good old 5U4s are REALLY easy to find, they came in all sorts of stuff. If there's any organ repair guys near you they should have lots of them for no more than $5 ea.
 
#4
BbbyBld said:
I've never tried it, but check out the text in the middle of this Invalid Link Removed.
Click to expand...

Ok, thanks. Mine is a 5AS4A though. That link found the info though. It's a Sylvania, but my RCA may be a Sylvania made for RCA
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I let it idle about a half hour and tried it out. Power tubes are brighter (not red) and the 5AS4A is brighter than the Sovtek. Amp is quieter too. I pushed it hard for about 3 minutes then put it on standby for about a half hour. Pushed it lot harder the second time around and no issues. Chassis isn't any warmer than it was with the Sovtek, so I guess it's good to go.

The bass response is better too. And what I thought may have been a speaker going bad might have been the Sovtek failing. Moments after a hard attack I was getting a fizzy rattle that would kind of rise into the sound. Anyhow, it's not there now :cool:
 
#5
jimbilly said:
My 'Tube Substitution Handbook' (tenth edition), says you can use a 5AS4A to replace a 5U4G. If you need more, good old 5U4s are REALLY easy to find, they came in all sorts of stuff. If there's any organ repair guys near you they should have lots of them for no more than $5 ea.
Click to expand...

Hi Jim, yes I've noticed they are plentiful. My RCA was in a '59 RCA Orthophonic phonograph console I bought at an estate sale. I found another '59, a smaller version last week. I've got 6 RCA 6BQ5/EL84's between the two of them as well.
 
#6
Really trying to do my homework on this. Am I correct in assuming the data suggests the 5AS4A is indeed an acceptable substitute ?

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What values on these data sheets is of most importance in determining substitutions ?

If I'm reading the data right on the tubes in question, it appears the 5AS4A is simply a more robust/efficient tube whereas the 5U4G has more sag.

Or am I way off base here ?
 
#8
johnk_10 said:
IME, those tubes are completely interchangeable. the 5AS4A is basically a little bit heavier duty version of a 5U4GB. the difference that you're hearing may be due to your 5U4 going bad. the two should be pretty close if they were both operating properly.
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Good enough. I'm pretty sure the Sovtek 5U4G is ready to fail. I'll toss it and go ahead and put my new tubes in it when they arrive.

Thanks to all who helped !
 

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