Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dwinstonwood on January 07, 2024, 11:52:35 am
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My current salary doesn't permit buying NOS tubes. So, I've been buying those "NOS various brands" tubes from AES, and TubeDepot, etc.
The JJ EZ81 in my Vox AC4 build seemed weak; the B+ voltages seemed low based on the (unloaded) 260VAC I measured on each side of the PT secondary (Hammond 270CAX). I was getting 262VDC at the reservoir cap.
So, I bought one of the NOS "various brands" EZ81's from AES, and it's a Mullard Made in Great Britain. It was made for Daystrom, and has the codes 347 and 1022 on it, but I don't know when it was made, or in which plant. Anyway, my B+ 1 is now 288.6VDC. I also added a $11.95 choke and there is now literally no audible hum in this amp.
I also had an issue where the Tremolo ticked when the Intensity was all the way up, but stopped when I backed it off a bit. I separated the Speed and Intensity ground point from the Tone and Volume ground star, and moved the Tremolo wires around. I was able to completely eliminate all of the ticking.
I'd be glad to learn anything about my Mullard, when and where it might have been made. Maybe it's an early 60's which would be a cool tube to have in my V-1-1 AC4. :icon_biggrin: Thanks.
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https://mullard.org/blogs/news/mullard-valve-etched-codes-how-to-interpret-them (https://mullard.org/blogs/news/mullard-valve-etched-codes-how-to-interpret-them)
https://www.effectrode.com/news/tube-enthusaist-tube-codes/ (https://www.effectrode.com/news/tube-enthusaist-tube-codes/)
https://www.audiotubes.com/mullcode.htm (https://www.audiotubes.com/mullcode.htm)
Not able to find correspondance
Franco
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Thank kagliostro! I appreciate your research.
I did find out that Daystrom LTD in Gloucester, England produced Heathkits for the UK market. Those numbers might have something to do with the kits. There are no etchings on the glass.
From the web site below,
"In the UK, Daystrom (Gloucester) produced UK versions of many of the [Heathkit] kits, using valves and components available here, transformers with 240V primaries etc. In the 1970s Daystrom moved into thickness gauges for the steel industry and in due course sold off the kit side to Cedar Electronics."
So, my tube would most likely have been manufactured before the sell-off.
https://www.vintage-radio.com/manufacturers-and-sets/heathkit.html
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... So, I bought one of the NOS "various brands" EZ81's from AES, and it's a Mullard Made in Great Britain. It was made for Daystrom. ...
... There are no etchings on the glass. ...
If there are no etched codes, then the tube is 100% Not-Mullard, no matter what the print says.
However, I think I see some etching obscured by the print, as noted in the cropped photo below. If the 2nd line starts with "B" or "R" then you've got a Mullard. The top line should say "8t" on an EZ81.
(https://i.imgur.com/JLihGDS.png)
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Thanks HotBluePlates. Great info. Even with a magnifying glass I can't find etching.
But, looking at several other examples online, mine does have the "D" getter with the two parallel wires, and the silk screening is exactly the same with the odd marks along the T's and F's. Also, the Mullard EZ81's that I'm looking at online don't have etchings, either. Although, other Mullards like ECC83's and EL34's do.
Here are some pics that are identical to mine.
I can definitely see people counterfeiting ECC83's and EL34's, but it seems like a huge amount of work for a rectifier that sells for $25. Either way, it's a much better tube that the JJ's I was using, and about the same price. :icon_biggrin:
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https://fuzzaudio.com/how-to-identify-fake-tubes#:~:text=Plate%20width%20and%20staple%20type,clones%20based%20on%20plate%20alone. (https://fuzzaudio.com/how-to-identify-fake-tubes#:~:text=Plate%20width%20and%20staple%20type,clones%20based%20on%20plate%20alone.)
Franco
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Thanks again kagliostro.
The "D" type getter in my tube agrees with that web site. It is close to parallel with the mica, and the silver coating comes down further from the top, like the real tubes.
Still there is no etching. So, I wouldn't resell it to anyone as a Mullard. Even though every other characteristic matches.
But... why clone a Heathkit (Daystrom) tube? :w2:
Thanks for the really useful info.
In the end, Tubes and More (AES) has been a first rate merchant in my experience. If this tube proves defective, I have a reputable business to contact for an exchange.