Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on April 28, 2025, 07:00:34 pm

Title: How to identify rectifier tube
Post by: punkykatt on April 28, 2025, 07:00:34 pm

Hello all, I was given a box of old tubes from Tv`s, radio`s, amplifiers, etc. Found one with no markings on the base or glass. Looked like it could be a rectifier tube by the plates. Checked with my meter pins 2 and 8 have continuity. Using my model 257 tube tester and going by the book that came with it and testing different  rectifier tube types here is what I got.
The scale that reads GOOD goes from 50 to 100.
Both cathodes read the same on all.
5Y3= voltage load 100 = 60 on scale
5R4=   "          "     60 = 59   "    "
5U4=   "          "     60 = 59   "    "
5V4=   "          "     30 = 50   "    "
5V3=   "          "     30 = 50   "    "
5W4=  "          "     30 = 50   "    "
5AR4= "          "     30 + 50   "    "


All the tubes have a heater currant of 2A or less except the 5U4 which is 3A.  By the voltage loads and scale readings can anyone determine which tube it may be?  Thank you for any help or advise.

Title: Re: How to identify rectifier tube
Post by: punkykatt on April 29, 2025, 09:19:23 am

Did power tube anode voltage testing using an amp comparing to known rectifier tubes.
GE 5y3 = 382v
RCA 5U4GB = 395v
Weber copper cap GZ34 = 409v
Sylvania 5AR4 = 413v
tube in question = 415v,  tube seated height= 2 3/4", glass bulb= 1 1/4" dia.

Title: Re: How to identify rectifier tube
Post by: tubeswell on April 29, 2025, 10:16:56 am

Quote from: punkykatt on April 29, 2025, 09:19:23 am

Did power tube anode voltage testing using an amp comparing to known rectifier tubes.
GE 5y3 = 382v
RCA 5U4GB = 395v
Weber copper cap GZ34 = 409v
Sylvania 5AR4 = 413v
tube in question = 415v,  tube seated height= 2 3/4", glass bulb= 1 1/4" dia.

Based on that, I’d totally guess it’s a GZ34/5AR4

Title: Re: How to identify rectifier tube
Post by: punkykatt on April 29, 2025, 10:29:25 am

Trying to determine the 5vac heater currant draw of the unknown tube. Can I connect my meter set to A/C voltage, black lead to ground and red lead to pin 2 of the rectifier tube socket, turn the amp on and measure the voltage? I know there high DCV there too. The amp being used for this test uses a 5y3 rectifier. Test with the 5y3 then with the unknown tube and compare voltages. If there is no voltage drop I`m going to guess it a 5AR4?

Title: Re: How to identify rectifier tube
Post by: tubeswell on April 29, 2025, 11:13:04 am

Quote from: punkykatt on April 29, 2025, 10:29:25 am

Trying to determine the 5vac heater currant draw of the unknown tube.

Try rigging a 1R 10W resistor in series with the filament winding and measuring the voltage across the resistor. If it measures 1.9V, bingo!

Title: Re: How to identify rectifier tube
Post by: punkykatt on April 29, 2025, 11:23:12 am

Thanks Tubeswell

Title: Re: How to identify rectifier tube
Post by: punkykatt on April 29, 2025, 02:39:53 pm

Got 1.4vac. good to go. Thanks again Tubeswell.

Title: Re: How to identify rectifier tube
Post by: tubeswell on April 29, 2025, 03:29:32 pm

Quote from: punkykatt on April 29, 2025, 02:39:53 pm

Got 1.4vac. good to go. Thanks again Tubeswell.

Well I’m still guessing GZ34 (because peak voltage is 2, so peak current is 2 too)

Title: Re: How to identify rectifier tube
Post by: punkykatt on April 29, 2025, 07:54:32 pm

5AR4/GZ34  agreed.