Advice on RCA 2A3 tubes for Allwave15

[David McGee]

I am still trying to repair my Allwave15.  During a slow power-up my two 2A3 tubes heated up normally.  But I found out that my speaker coils are bad and I am getting it rewound right now.  In the interim I tested both 2A3 tubes for "merit" on my Eico 666 tube tester they both pegged the needle past "Good".  All other tests were normal.  I've heard conflicting comments on what that means.  Are these tubes likely good or bad?  If bad can I substitute new Soviet 2A3 tubes since they are much cheaper?

THANKS, David

[David C. Poland]

double check your tube testor settings, especially the filament voltage selection control.. Do you have any other 2A3 tubes  for comparison?

or any other 2.5 volt  tubes.  What happen testing a 6 volt output tube - results seem normal?

Your mains voltage high? like much over 120 volts? A good meter to verify your tube tester is supplying 2.5 volt to the tube?

Never tried any Sovtech tubes, but they should be satisfactory - but someone else will chime in hopefully.

[David McGee]

Thanks for the good suggestions.  I did recheck the tester settings.  The filament is 2., the grid is 17 and the plate is 82.  I don't have any other 2A3s other than these two that were already in the power amp.   I also did check type 56, 57 and 58 tubes for the radio that all have a 2.5 setting for the tester and they checked out fine.
I also checked a 5z3 at 5 volts and it  checked out good.  I don't have a 6 volt tube to try.  If the 2A3s are not good would it potentially harm the radio when I do another gradual power up with dim bulb/variac?

David C. Poland said:

double check your tube testor settings, especially the filament voltage selection control.. Do you have any other 2A3 tubes  for comparison?

or any other 2.5 volt  tubes.  What happen testing a 6 volt output tube - results seem normal?

Your mains voltage high? like much over 120 volts? A good meter to verify your tube tester is supplying 2.5 volt to the tube?

Never tried any Sovtech tubes, but they should be satisfactory - but someone else will chime in hopefully.

[David McGee]

Also, my main voltage from the wall is 121.9v

David C. Poland said:

double check your tube testor settings, especially the filament voltage selection control.. Do you have any other 2A3 tubes  for comparison?

or any other 2.5 volt  tubes.  What happen testing a 6 volt output tube - results seem normal?

Your mains voltage high? like much over 120 volts? A good meter to verify your tube tester is supplying 2.5 volt to the tube?

Never tried any Sovtech tubes, but they should be satisfactory - but someone else will chime in hopefully.

[David McGee]

I misstyped the filament voltage setting I used.  It is 2.5.  

David C. Poland said:

double check your tube testor settings, especially the filament voltage selection control.. Do you have any other 2A3 tubes  for comparison?

or any other 2.5 volt  tubes.  What happen testing a 6 volt output tube - results seem normal?

Your mains voltage high? like much over 120 volts? A good meter to verify your tube tester is supplying 2.5 volt to the tube?

Never tried any Sovtech tubes, but they should be satisfactory - but someone else will chime in hopefully.

[David C. Poland]

Pegging the meter rather than merely exceeding the target reading for a new tube seems very wrong. Seems unlikely both tubes are off the chart high. Are they the same brand and a US brand like Sylvania, RCA, TungSol etc?But, because you had the same result for both tubes, seems the fault may be with the tube tester.

And the tubes are clearly marked 2A3 on the glass somewhere? 

[Kent King]

It may be the settings for the tubes on that tube tester...you will not harm the set unless the tubes show a short. Given the cost of 2A3 tubes, I would still try them in the set.

Regarding the SOVTEK 2A3s, most folks report adequate results, some have said they can be microphonic. I've not tried any personally...

Kent

[Norman S Braithwaite]

It is not unusual for consumer grade emission type tube testers to pin the meter on strong tubes.  Of potential concern, however, are misaligned elements and gas which can both cause a tube to have higher than normal emissions.  Misaligned elements can cause a hot spot that sometimes in high power output tubes results in a red area on the plate but the tube will still be usable if the plate does not go red.  Gas in the tube can cause the tube to draw excessive current resulting in potential damage to the output transformer and power supply.  Gas in the tube will cause the area within the plate structures to glow blue.  If this is the case, the tubes should be replaced.  Blue glow on the outside of the plates or on the glass envelope is not gas but is an indication of a robust tube.  It is unlikely, however, that both tubes would have the same defect.  It is much more likely that the pinned meter is a characteristic or defect in the tube tester.

Norman

[David C. Poland]

I forgot your title stated RCA brand 2A3's. RCA would be high quality tubes and a favored brand if you were to observe sales on eBay.

The RCA's are replacements, so newer than the radio and probable good. All indications are that Scott originally supplied either Arcturus or, for later production, Sylvania brand tubes for the AW-15.

[Troy Taylor]

Hello-

I have been using a quad of LinLai 2A3s in my AW23 for years with very good results, despite being the least expensive version of the current Chinese production.  I had plenty of reservations, but decided to go for it anyway and bought them when the new price was $75/ea.  After more than 4 years of regular use (not less than weekly, typically for several hours minimum), they are still operating like new.

The only catch is that these particular tubes are made with glass envelopes that have the same size as the 300B, which is larger than a "normal" 2A3.  This means that the four tubes do not fit in the standard socket spacing on a Scott amp.

To accommodate this larger size I built two socket extensions that raise up one pair of the tubes.  They fit well with this staggered arrangement.  The bases were salvaged from dead 5Z3 or other 4 pin tubes, and the female sockets are inexpensive.  The height of any ordinary 4 pin tube base is plenty sufficient for clearance with these larger tubes.

I have a set of Electro-Harmonix 2A3s stashed in reserve (supposedly an upgrade from Sovtek, but made in the same plant by the same company in Russia) but I have never tried them.  

-Troy