SET Asylum

Identify Damaged Welborne Labs 300B Laurel II Power Transformer Part Number

47.204.128.68

jbelt824@gmail.com

A

The power transformer on my Single Ended Triode tube amplifier was physically damaged and the bell end needs replacement.
The transformer is from a: Welborne Labs Laurel II SET 300B monoblock amplifier
- Hammond custom power transformer: 350-0-350-5-6.3, 120Vac / 60Hz, Classic Design, Manufacture date: 1994/1995. Not sure yet if the transformer works as it was damaged in shipping.
Hope someone can help me. I have contacted Hammond Mfg. and they require a part number in order to assist me. Thanks, Jim

Follow Ups:

Try looking at the Antique Electronic supply catalogue - richardl 16:44:23 04/20/23 (4)
I found some Hammond info searching for an old transformer. It may have been made for a completely different purpose and Welborne used it.

YOu are looking for 350-0-350 with what amperage? maybe 200mA?
The 5v probably matches the needs of the 5AR4 which is about 2-3 amps
The upper 6.3v is probably lower than 2A
and the lowest 6.3V must be at least 2 amperes

You can for a transformer that has the same 350-0-350 and a 5V/2A(or 3A) and 2 different 6.3V and probably both at 2 amperes.

If no one has an answer, I would start looking at AES because they still sell the older model Hammonds as guitar replacement power transformers etc.

Good luck.
- RE: Try looking at the Antique Electronic supply catalogue - jbelt824@gmail.com 04:49:04 04/21/23 (3)
  Appreciate the response. Due to my limited knowledge of tube amps coupled with their high voltage, I think my best next step is to take the damaged monoblock into an expert and have the transformer tested. If it works, I'll just have the end bell damage / replacement to deal with. If it doesn't, not sure what I will do, but I'll deal with that if & when the time comes. Thanks again.
  - RE: Try looking at the Antique Electronic supply catalogue - D Mike 06:19:59 04/22/23 (2)
    This one is close but it only has one 6.3 volt winding. Dimensionally it may be the same if you just need to order an end bell.
    - https://www.hammfg.com/files/parts/pdf/373DZ.pdf (Open in New Window)
    - RE: Try looking at the Antique Electronic supply catalogue - D Mike 07:45:38 04/22/23 (1)
      Could you clarify if your amps are monoblocks or the stereo version that is described as "dual mono"? If it's the dual mono stereo version, then you need a lot more current than the transformer spec sheet that I posted.
      
      It's very possible that Ron had custom transformers built to his spec by Hammond.
      - RE: Try looking at the Antique Electronic supply catalogue - jbelt824@gmail.com 14:35:15 04/23/23 (0)
        
        In Reply to: RE: Try looking at the Antique Electronic supply catalogue posted by D Mike on April 22, 2023 at 07:45:38
        
        Mike, they are the 2 monoblocks (Laurel II). The stereo version was simply called the Laurel.
I've got the Assembly Manual - Does that help ? ...............nt - Cut-Throat 13:50:40 04/20/23 (6)
nt
- RE: I've got the Assembly Manual - Does that help ? ...............nt - jbelt824@gmail.com 15:14:01 04/20/23 (5)
  Cut-Throat, thanks for the response. I also have the manual. Just hoping that someone more knowledgeable than me (I am a novice) might know the original part number or know of a modern day drop-in replacement based on the power supply schematic. I hate to think that if a power transformer goes bad, that this beautiful tube amplifier becomes a boat anchor.
  
  Power Transformer: Hammond power transformer: 350-0-350-5-6.3, 120Vac / 60Hz
  Mounting: Lay Down
  Mounting Centers: 2 1/2" X 3 1/4"
  
  Jim
  - RE: I've got the Assembly Manual - Does that help ? ...............nt - richardl 09:42:46 04/24/23 (4)
    Power Transformer: Hammond power transformer: 350-0-350-5-6.3, 120Vac / 60Hz
    Mounting: Lay Down
    Mounting Centers: 2 1/2" X 3 1/4"
    
    This may be enough for a tech to check the catalogue. Hammond does not change the tube power transformers all that often. You can find this.
    
    The Amperages can be found with the above information about voltages plus the knowledge of its size. That will tell you the Amperage of the 350-0-350, which will solve your problem.
    
    Good luck.
    - RE: I've got the Assembly Manual - Does that help ? ...............nt - Paul Joppa 10:24:13 04/24/23 (3)
      It looks very much like the Hammond 373X, except the amp needs two 6.3v windings and the 373 has only one. So it may have been a custom design.
      - RE: I've got the Assembly Manual - Does that help ? ...............nt - jbelt824@gmail.com 13:17:10 04/26/23 (2)
        
        In Reply to: RE: I've got the Assembly Manual - Does that help ? ...............nt posted by Paul Joppa on April 24, 2023 at 10:24:13
        
        Thanks one and all for the great responses. I took the monoblock amp into an audio repair shop in Tampa and they said the transformer still works properly. I measured the end bell dimensions and found what I hope is a good match from a company in China. I took a shot and order it. Hopefully it is close enough that I can just do a few alterations to make it work.
        
        Paul, I got a response for Hammond Mfg. and they confirmed it is indeed custom made. They also let me know they can't help me with a replacement.
        
        Thanks again.
        
        RE: I've got the Assembly Manual - Does that help ? ...............nt - Paul Joppa 21:13:50 04/26/23 (1)
        
        In Reply to: RE: I've got the Assembly Manual - Does that help ? ...............nt posted by jbelt824@gmail.com on April 26, 2023 at 13:17:10
        
        Thanks for posting the information. I suppose Hammond has a proprietary agreement with Welborne - it's not uncommon.
        
        I believe the end bell is for EI-125 laminations, in which case you can also source them from Edcor (see link).
        Edcor end bells (Open in New Window)
        
        RE: I've got the Assembly Manual - Does that help ? ...............nt - jbelt824@gmail.com 08:08:28 05/01/23 (0)
        
        In Reply to: RE: I've got the Assembly Manual - Does that help ? ...............nt posted by Paul Joppa on April 26, 2023 at 21:13:50
        
        Wow! They are the same structure for sure. If the ones on order from China don't work out, I'll certainly give these a shout. Thanks again.

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