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Mystery 12AU7 = RFT

66.32.67.236

I've had a couple of mystery 12AU7s for a while, and I decided to see if I could figure out who actually made them.

Both are labeled Hewlett Packard by Amperex, but one shows Germany as the country of origin, while the other claims Gt. Britain.

A Google image search revealed them to be RFT production, one marked 7-51, the other 9-51. (1967? 1969?)

Perhaps these should be called Flat Tops since the top of the envelope is noticeably flatter than other makes.... And I notice that these seem to get positive reviews.

David

Follow Ups:

RE: Mystery 12AU7 = RFT - tvr2500m 21:37:41 07/03/09 (0)
Nice tube. It's the OE tube Conrad-Johnson fit in their PV-12/L/A/AL preamp, a preamp which I happen to own and enjoy. I'm not sure what these codes mean either. I've seen some of the Eastern European sellers making manufacturing date claims for these tubes indigenous to their part of the world, which kinda appears that they seem to have some insight into decoding these codes. Though maybe they're just makin' it up ;)
Early 1950s would be WAY too early for these. I surmise from my own sleuthing and ownership of several varieties of RFT ECC82s that this tube with the single heavy-duty getter support and small halo getter is the final version of this RFT tube. It dates to the 1970s, and could have been produced into the 1980s.
Yeah, RFT ECC82s and ECC83s all have these small, 12AT7-like plates. Some Tungsrams have plates like this, too, but there're enough differences to distinguish all from one another (including the Tungsram "tag"). Identification of whether an RFT is an ECC82 or an ECC83 could be a little more work in the absence of their delicate silkscreened type markings.
So, double, maybe even triple, branding - HP, Amperex, and RFT? Interesting and curious. Maybe these particular tubes were supplied by Richardson to HP as Amperex-branded. I've got some ECC82 10Ms that're RFTs. Gotta be Richardson?
It's very handy to be able to make a positive tube ID, but it can be plenty convoluted, even for folks more familiar with these things. Raytheon-branded Japanese-made tubes that still wear the Raytheon EIA code (which makes sense as Raytheon is the final supplier in the chain?). Amperex Bugle Boy "Made in Holland" silkscreened tubes that have Valvo Philips codes (which has to trump the silkscreening, right?). And on, and on. Fun, right?
I really like all the RFT ECC82s and ECC83s I've used. Both have typically sounded on the "neutral" side of things in most of the systems I've used them in. Clean, clear, extended, and tidy. (did I just write "tidy"? ;) )
- SJ

Edits: 07/03/09 07/04/09
HP date code conventions..... - doodlebug 08:09:43 07/01/09 (0)
If those are, indeed, HP date codes, here's the convention that was adopted company-wide back in the 60s:

For service purposes, date codes would be labeled as year then month. The year number posted would be added to 1960 then followed by a 2-digit number of the week of that year.

Thus, 7-51 would translate into the 51st week of 1967. I'm not clear that this convention still stands for today's gear as I got out of the hardware world there back in the early 90s and HP got out of manufacturing in the 90s. They're pretty much an assemble-from-subcontracted parts these days.

If you need more details, there is an HP/Agilent group at Yahoo for old test gear. Many of the old engineers still hang out there.

Cheers,

David
Retired HP, '85-'05
RE: Mystery 12AU7 = RFT - CV4109 21:52:04 06/30/09 (4)
A Google image search revealed them to be RFT production, one marked 7-51, the other 9-51. (1967? 1969?)

- RFT/East German Small Signal tubes have a peculiar glass bottle that is easy to recognize if you see enough examples.

- If your tube looks like RFT, then it is. Production could be anywhere from 1960s-1980s. 7-51, the other 9-51 numbers do not relate to the actual production years. If you can post pictures, it will be easier to confirm the decade.

These are not Mullards or Amperex for sure. Decent tubes otherwise.
- RE: Mystery 12AU7 = RFT - Thermionic27609 14:05:58 07/01/09 (3)
  Yes, there's no mistaking the RFT tubes for anything else. The construction is very distinctive: folded plates more like some 12AT7s with three holes and a very heavy-duty getter support. Tube envelopes are large in diameter with unusually flat tops.
  
  I find it difficult to get a good tube photo with my digital camera, but here's a link with one with the exact construction. The labeling is the only difference.
  
  With the date codes, I would think they would be 1960s or maybe 1970s. Was RFT still making these in the 1970s? That might explain why they're Amperex labeled with their East German origin disguised. Or would Hewlett Packard have been making anything with tubes in the late 1970s?
  - Late 1970s production - CV4109 16:26:33 07/01/09 (2)
    HP did not make tubes.
    
    These would be late 1970s-early 1980s RFT E. German production. Similar to these in the link below:
    - RFT ECC82 Single Support Halo - East Germany (Open in New Window)
    - RE: Late 1970s production - Thermionic27609 22:17:18 07/02/09 (1)
      CV4109,
      
      What I meant was: was HP producing anything that used vacuum tubes in the late 1970s? Or were they simply supplying HP branded tubes as replacement parts?
      
      David
      - RE: Late 1970s production - CV4109 16:59:03 07/03/09 (0)
        
        In Reply to: RE: Late 1970s production posted by Thermionic27609 on July 02, 2009 at 22:17:18
        
        Perhaps some RF/Microwave/Instrumentation gear using tubes was still being made in late 1970s by HP but not totally sure. Since tube based instruments like scopes, signal generators etc. were in use through 1980s in labs across the country, there was a lot of service components in the distribution channel.
        
        Tubes were still being made until mid-1980s by companies like Tungsram, RFT, BEL India etc.
RE: Mystery 12AU7 = RFT - Michael Samra 21:00:11 06/30/09 (4)
David
The dates would reveal July 1951 and Sept 1951.Amperex could be made in germany or Holland but the other would be a Mullard.Are there creases in the top of the tubes.
If the power supply waveform isn't pretty,neither is the sound in most cases.
- RE: Mystery 12AU7 = RFT - Tom Bavis 07:48:40 07/01/09 (0)
  I would read those dats as 1967 ('77?), week 51 and '69 (or '79) week 51. HP labeled those codes, so manufacture date will be a little earlier - any etched codes?
- Not likely - CV4109 21:58:33 06/30/09 (2)
  Have not seen 1951 Amperex or Mullard ECC82 so far.
  - RE: Not likely - Michael Samra 22:35:28 06/30/09 (1)
    Not likely
    I agree but those dates you gave would indicate that.Do you have the actual tubes in front of you?.I have never known the europeans to use date codes the way used to with the last two digits being the year.
    If the power supply waveform isn't pretty,neither is the sound in most cases.
    
    Edits: 06/30/09
    - RE: Not likely - FenderLover 06:09:02 07/01/09 (0)
      I was under the impression that Philips was the first to make the ECC8X series tubes in Europe & they didn't start-up until the mid-1950's. My earliest ECC82 are some Mullard ECC82 dated the usual Philips/Mullard way to around 1958.

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