[fado]

For its LS 100 preamplifier, Modwright Instruments suggests Mullard, Amperex or Phillips ‘GZ34’ tubes as upgrades. In addition to the brands mentioned above, these NOS tubes were sold under a variety of other brands such as Valvo, Adzam, Dario, Bogen, Scott, Pilot, etc. If I am shopping for mid-1950's to mid 1960's versions of these tubes, is there going to be a sound quality difference between a Mullard or Philips branded tube verses an Adzam or Valvo or xxxx branded tube given equal condition?

Thank You

[adrianc]

For its LS 100 preamplifier, Modwright Instruments suggests Mullard, Amperex or Phillips ‘GZ34’ tubes as upgrades. In addition to the brands mentioned above, these NOS tubes were sold under a variety of other brands such as Valvo, Adzam, Dario, Bogen, Scott, Pilot, etc. If I am shopping for mid-1950's to mid 1960's versions of these tubes, is there going to be a sound quality difference between a Mullard or Philips branded tube verses an Adzam or Valvo or xxxx branded tube given equal condition?

Thank You

They are all the same valves and have the date code F31,F32,F33,
Adrian

[avahifi]

If you can figure out how to do it safely, measuring the output voltage of your pet 5AR4 tube will provide you more useful information than just guessing about how it might be affecting the sound of your amplifier.

I have seen various brands have more than 20 percent  variation in output voltage and this will make a huge difference in the way the audio circuit behaves.  Given a normal power transformer the DC output of a 5AR4 tube after the first big filter capacitor will be somewhere between 350V and 450V DC depending upon the brand and age and heater voltage.  In many circuits a low output 5AR4 will cause the output tubes to nearly turn off.  The bias current will sag, and the amp will sound muddy and probably not reach full power.  A very high voltage output 5AR4 will turn the circuits on much harder (in some circuit designs, too hard) and that can give you harder and brighter sound than you really like.

Check with the designer of your amplifier if you can and ask him what voltage range he suggests as best for his circuit design.  This is a lot easier task then just listening by ear to a bunch of different 5AR4 tubes without measuring and trying to find the "golden tube" by ear.  The problem with this approach is that you probably won't be able to do this twice.

By the way, with the AVA Ultravalve and Ultimate 70 we would like to see a high output 5AR4 used if possible, with an output DC voltage of about 450V. After the tube there are multiple regulated power supplies, so the actual output voltage is not critical as long as it does not sag below 400V.

Regards,

Frank Van Alstine

[medium jim]

Frank:

Well written, the rectifier acts as a battery.

Jim

[fado]

Adrian:  Thank You for the reply. Can the f31, f32, f33 designations alone tell the date or are these tube types which indicate a date range?

Frank:  Thank You for the very in-depth reply. Unfortunately, I did not understand the part of your reply that said, “The problem with this approach is that you probably won't be able to do this twice.”

[avahifi]

I was suggesting that if you choose rectifier tubes by listening only, it is very unlikely that you would twice choose a 5AR4 with very close voltage output to each other.  Too much guessing in the process.

Now signal tubes, that is a whole different can of worms.   

Regards,

Frank

[adrianc]

Adrian:  Thank You for the reply. Can the f31, f32, f33 designations alone tell the date or are these tube types which indicate a date range?

Frank:  Thank You for the very in-depth reply. Unfortunately, I did not understand the part of your reply that said, “The problem with this approach is that you probably won't be able to do this twice.”

Hi fado the F31 is the factory code also have a manufacture date like B8D which means from Blackburn 1958 April.
Regards
adrian

[plasmapan]

They are all the same valves and have the date code F31,F32,F33,
Adrian

Dear Andrianc,

I've been reading your various posts about the GZ34 and I read you find the F31 better than the F33, F32 and even Metal Base rSB/rS1 : could you please explain where the F31 is superior?

Thank you so much,
Gianluca