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5f4 Super and 5e7 Bandmaster questions and transformers

Discussion in 'Glowing Bottle Tube Amp Forum' started by theprofessor, Jan 8, 2019.

  1. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    I have documented observations of one of my 1959 5E7’s. The choke number was 14684. I did a search for the specs and came up with this thread from the Music Electronics forum. Check out the second post. The poster gives the specs for the 14684, which he says he doubts was used in this amp. In contrast to the 200 ma choke that is usually accepted as ‘proper’, the 14684 is a 90ma choke. Classic Tone offers such a choke.

    https://music-electronics-forum.com/showthread.php?t=7038

    I have no idea what difference would occur due to the difference in the specs, but I know what was in my Bandmaster.

    http://www.classictone.net/40-18003.html
     
  2. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Wally - That's fascinating. Given that you've seen a '59 5e7 with that particular choke, it's no mistake. And I assume it was wired per the 5e7 schematic, rather than between the OT center tap and the screen grids. I would love to know which other chokes came in that amp, and if they were always under-spec'd like this or whether there were chokes that were actually built to handle all the current in that position.

    I noted on that page you mentioned that Bruce Collins of Mission Amps said he formerly used a Hammond 158Q choke (5Hy, 150 mA) in his 5f4s, 5e5s, and 5e7s. As of the time of that post, he said he was getting Heyboer to custom-wind a choke that was 5Hy and 200 mA. Now the similarly-spec'd Hammond 159S (4Hy, 225 mA, 65R) can do that job too.
     
  3. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    Well, we may have stumbled upon one of the most discussed and unsettled topics in Tweed amp history - choke specs.

    Here is from a thread on ampgarage (forgive me if it's been posted already). It's for a Tweed Twin, but MM's clone for it is certainly higher than a 90mA choke, and they said the parts varied, so who knows what was standard:
    I got the specs on the choke used to build my 5E8-A Twin. It's made by Mercury Magnetics, this is what they sent me:

    "The FC-TTWIN is approximately 60 ohms, 150 ma, and 3.5 H. These are approximate. Also, the originals in Fenders varied. We chose this one from an original for its tone." https://ampgarage.com/forum/viewtopic.php?f=6&t=5254&sid=ce42af781093650d90e48d1e6b8861bd&start=15

    Weber's Tweed choke by Heyboer is a 125mA choke based for the 14684. Again, higher than the standard 90mA Fender choke from later years.
    https://www.tedweber.com/hy014684

    And this Guitar.com article about restoring a 6v6 Tweed Super has a chassis pic and specified it's the 14684 choke. The thing is a hella lot bigger than the OT. Granted, it's a 6v6 model, but the 8160 PT was a big transformer, and the choke on this thing dwarfs the OT.

    5e choke.png
     
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  4. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Prof, I owned those two Bandmasters and the low power Twin before I started working on amps. This was 25 years ago. In that pre-internet era, I was buying and reading magazines and books and learning about these vintage amps that way and through hands-on experience of identifying/dating them by codes...old school. Buying and selling will make a cautious person who understands those details...caveat emptor. And.....caveat vendor. I didn’t want to lose money or cheat anyone by selling misrepresented items..whether through intent or ignorance.
    I knew a very good tech and he did all of the work I needed done...no matter what the problem. He offered to explain things to me, let me watch, work alongside. I did watch him work some...but I should have availed myself of his offehr. When he left town, I became a tech by default after having two BF amps worked on by two different young men who knew some formal electronics...associate degrees for both in electronics. I had to finish both jobs...so I started doing amp work. So....I never studied those circuits in those amps to the point of noting the placement of the choke. I was so naive to think that what I was seeing on the schematic was what was there and there were never any variance. I knew enough to be able to ascertain dates and originality....but I didn’t study actual circuits in an6 depth at that time....beyond schematics. I was thinking after my last post that you would be asking that question! (;^). I wish I had known then what I know now......
    I remember looking at an amp on his bench while he was identifying this or that aspect of the circuit..without a schematic. I knew I had a long way to go....still ain’t all the way there....never will be. However, I can look at an unknown circuit and get a fair idea what is there. Ex: I have a ‘homebuild’ tweed cabbed 2x10 combo here. It looks like someone ordered a cab and chassis for a 5F4 Super.....built they didn’t build that amp. It appears to me that there is a Marshall Md. 1987 circuit sitting in that chassis...but missing the middle tone control circuit. Pity that missing control, eh? Nice looking build...whoever did it.
    Good luck on the build, Prof. I’ll follow along...interested I am.
     
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  5. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Yes, this notion of a "standard" is interesting. For example, we know for a fact that some 5e7s used very small chokes (rated for 90 mA current) as choke input filters to handle the entirety of the amp's B+. We know because Wally has seen one. And yet it seems that some of these same amps had much bigger chokes that could handle the current better in that position.

    If we take anything that Mercury Magnetics makes and calls "tone clone" as a guide, we can deduce that 5e7's sometimes had 2.67R output transformers, sometimes had 4R output transformers, sometimes had 2R output transformers, and sometimes had output transformers with multiple taps--2R, 4R, and 8R. And this is only to focus on one spec of those OTs.

    https://www.mercurymagnetics.com/pr...bandmaster&pa_product-type=output-transformer

    We also know that while the 5e7 (and 5f4) schematic and layout lists a B+1 of 415V, the PT's often ran them much hotter. For example, when I spoke to the fellow at Mercury Magnetics the other day, I asked him about their various 5e7 power transformers. I indicated that I wasn't looking for lots of clean headroom. He recommended one of their power transformers that is a clone of a 5e7 PT. It's a 360-0-360V PT, and it's labeled as "lower B+." (!). If they're cloning a 360-0-360 PT from a 5e7 and calling it a "lower B+" relative to some other clones of 5e7 PT's they've made, I cannot imagine what some other of their PT's put out, voltage-wise!

    https://www.mercurymagnetics.com/pr...=bandmaster&pa_product-type=power-transformer

    The folks at Mercury Magnetics view this simply as part and parcel of the reality of cloning parts of vintage Fender amps. Not only did Fender simply use whatever is available, it sounds as if their transformers did not all conform to tight tolerances, spec-wise. I suppose that means a 5e7 (and probably most other Fender amps as well) are really more like a family of amps that conforms more and less to the paper specs of the model. But they're all 5e7s.
     
  6. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Prof, regarding that multitap OT from MM. I am going to think that is not a clone of an original transformer in a Fender but rather is an adaptation to yield multiple tap options with a similar result as the single impedance OEM transformers found in these various vintage Fenders. Although I haven’t seen everything, I have never seen or heard of a vintage Fender tweed with a multitap OT. That adaptation would be a useful thing for modern players who might want to build a head version and be able to use different speaker arrangements, I would think.
    Thinking about it, IF Fender had gone to the multitap thing for an OT, they could have covered three if not four amps wth a single OT....5E5A, 5F4, 5E7, and perhaps the 5E7Twins.
     
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  7. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Back to the issue of choke placement and sonics I raised in post # 57:

    I corresponded with a couple of folks over at TGP who said on this thread that they preferred the sound of the smaller choke after the power tube plates rather than the bigger tube before the plates. I asked specifically what the sonic difference was.

    One member seemed to recall that putting a smaller choke between the OT center tap and the screen grids, just as in the 5f6a Bassman and others, produced better bass response. He noted that Mark Norwine also prefers the smaller choke between the OT center tap and the screen grids in a 5e7.

    Another member said that "a smaller choke after B+1 creates a much more responsive amplifier, at the expense of stiffness."

    I find the whole thing fascinating, especially in light of Fender's changes to the 5e7 in their 57 custom Bandmaster reissue. I found a thread on The Fender Forum where SoK66 notes the main changes to the 57 custom Bandmaster reissue. I think I'm remembering them correctly:
    (1) rectifier is a 5AR4/GZ34, instead of a 5U4
    (2) B+ is higher--around 455V
    (3) a 10k bias pot
    (4) a 12ax7 in V1 instead of a 12ay7
    (5) 22uF filter caps instead of 16uF filter caps

    The goal, apparently, was to try to stiffen the thole thing up a bit with the 5AR4 and higher voltages. And others are making clones with chokes after the OT center tap so as to avoid stiffness. It's all very confusing, since the 5e7 is typically referred to as a very touch-sensitive amplifier.

    Another effect of the choke later in the circuit will likely be more noise/hum, since one would have to double the B+1 cap and then the cap will do more of the filtering. If I understand correctly, they tend to be noisier at that job than a filter choke.
     
    Last edited: Jan 13, 2019 at 9:29 PM
  8. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Good point, Wally. Thanks.
     
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  9. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    I found the schematic for the Fender 57 Bandmaster reissue. They use a huge choke and put it before the plates, just like the old Fender schematic.
     

    Attached Files:

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  10. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    I just thought about my post with the chassis picture and the size of that choke. For a comparison, here is a (all Hammond) Deluxe Reverb OT (6.6k, 20 watt), a 90mA Fender-style choke, and a Tweed Deluxe OT (8k, 15watt). So, the choke on that 6v6 Super above was much bigger than the OT, and this 90mA choke is the same height and a half inch thinner than the 15 watt 5e3 model.

    [​IMG]

    Sent from my XT1585 using Tapatalk
     
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