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Old 14th July 2010, 06:19 PM   #1
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Thumbs down Help finding a tube tester for Stereo tube amps.

Good day,
After swapping DACS and modding CD players I want to get in to Tubes.

I just finished refurbing a Magnavox 9302-00 f or a friend and really like the sound. I plan to get something similar myself. (6BQ5's and 6EU7's)

I want to get a tube tester and there is a Radio City Model 802N available locally.

Will it work with this series of tubes or is it too old? Will start out with Stereo tube amps form the late 50's early 60's.

Thanks!
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Old 14th July 2010, 07:46 PM   #2
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by Fasterdamnit View Post
Good day,
After swapping DACS and modding CD players I want to get in to Tubes.

I just finished refurbing a Magnavox 9302-00 f or a friend and really like the sound. I plan to get something similar myself. (6BQ5's and 6EU7's)

I want to get a tube tester and there is a Radio City Model 802N available locally.

Will it work with this series of tubes or is it too old? Will start out with Stereo tube amps form the late 50's early 60's.

Thanks!
Don't put to much trust in tube testers, unless you have a tube tester tester to verify the testers calibration. If you are using only a few types of tubes you can make a test jig with a tube socket, some resistors and a power supply and use your multimeter.

Even with a good tube tester you still don't know about the tube until you put in to an amp the measure it there. that is why I said the test jig.

This is different if you are working as a general service and repair tech one a wide range of tube based equipment. But for just power tubes you simply put the voltage(s) and resistor loads on them, apply a signal the look at the result. This is 100% fool proof. and near zero cost.
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Old 14th July 2010, 07:48 PM   #3
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How about a quick schematic and some numbers or a source for them?
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Old 15th July 2010, 03:19 PM   #4
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Just follow the recommended operating points in your tube manual.
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Old 15th July 2010, 10:56 PM   #5
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Default good tubes, bad tubes

Uh, I just replaced the capacitors in my PAS2 preamp, to eliminate channel imbalance. I had measured the resistors and they were fine, and swapping the tubes L-R didn't help. After replaceing the 1982 power supply capacitor with a new one, I'm measuring 120 VDC on the last plates in the chain that are supposed to be 210 V. But t sounds great! I put new metal film plate resistors in, it cut hiss a tiny bit. But the numbers are wrong. The interstage capacitor b+ resistors measure fine, and I replaced the first stage resistor with a RN55 metal film and the low voltage stage resistor with a new 47K 2W metal film resistor made in india that measured okay cold. Three of the 4 12AX7's are 1961 vintage, one RCA I bought in 1975. The low voltage B+ circuit is on old 12AX7's in the high voltage (1 V input) stage. Does this mean my 12ax7's are leaky? The first stage capacitor voltage out of the rectifier is correct, so the 1975 rectifier is still okay, I think.
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Last edited by indianajo; 15th July 2010 at 11:01 PM. Reason: resistor measurement.
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Old 16th July 2010, 08:20 AM   #6
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if its 120, its 120, not 210. Thats wrong. So, why?
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Old 18th July 2010, 07:05 AM   #7
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Yeah, 120 VDC B+ instead of 210 is wrong, why is my question. Source voltage from rectifier is right, dropping resistance is new and right, sound coming out is right, quiescent current is too high. Would cost me $34 to buy 2 new tubes and try them. I was hoping somebody here knew something about 49 year old tubes that draw too much current.
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Old 18th July 2010, 09:07 AM   #8
Ian444 is offline Ian444  Australia
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indianajo, it's unlikely the tubes are the problem, more likely the resistor/s associated with the old tube/s. Proly best to start a new thread for your questions and post a schem.

Ian.
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Old 19th July 2010, 01:43 AM   #9
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by indianajo View Post
Yeah, 120 VDC B+ instead of 210 is wrong, why is my question. Source voltage from rectifier is right, dropping resistance is new and right, sound coming out is right, quiescent current is too high. Would cost me $34 to buy 2 new tubes and try them. I was hoping somebody here knew something about 49 year old tubes that draw too much current.
If tubes are drawing to much current, it's not the tube's fault. It's the way the tube is biased. Look at your bias voltage and then check the tubes's data sheet. Data sheets are easy to find here:
TDSL Tube search One of the things that fail is if a pot is used to set bias.
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