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Tweed Bandmaster clone OT

Discussion in 'Amp Tech Center' started by Doc Simons, Apr 19, 2017.

  1. Doc Simons

    Doc Simons TDPRI Member

    Age:
    63
    4
    Apr 4, 2017
    South Carolina
    Hi. Just finished my one-12 combo with a 5e7 circuit. I ran across info indicating Leo often undersized his output trannies to produce a lot of punch. My son's Vibolux at 35 watts is the same circuit as my 40 watt Super, but with a very small OT. Both are great, but very different character, especially bass and volume/headroom.

    Anyway, I put an old Deluxe Reverb OT in the 5e7 with amazing results. More headroom, lots of punch. Of course, similar to my Deluxe, but has a tweed vibe, touch sensitivity.

    Thee are only two mods: an off-stby-on switch instead of separate toggles. I also swithed the 250pf coupling cap to 500pf. It allows more mids through. Just thought I'd share that for you builders.
     
  2. screamin eagle

    screamin eagle Friend of Leo's

    Oct 9, 2008
    S. CA
    While the results are the same, I'm inclined to think that Leo chose smaller OT's from a "Don't over-engineer and increase costs" perspective.
     
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  3. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Fwiw, smaller OT's do NOT produce more 'punch'. They saturate earlier than would an OT with more iron....breakup earlier and have more of a 'singing' quality at lower volume than would a bigger OT. Larger OT's yield more 'punch', better articulation, and more power output.
    Leo understood this well. That is why the 5F6A Bassman and the 5F8A Twin both yield more power, more punch and better articulation at volume. The same difference exists between the 'small OT' 6L6 Bf/Sf Fenders such as the Bandmaster, Pro, Pro Reverb, Vibroverb, Vibrolux Reverbs and the Bassman and Super Reverb.
     
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  5. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    ?

    [​IMG]
     
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  6. mRtINY

    mRtINY Tele-Afflicted

    May 7, 2015
    Orygun
    Only one in that amp seems to be the one connecting the Treble pot to the output of the cathode follower... Makes sense that you'd get more mids ...
     
    Last edited: Apr 19, 2017
  7. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    I've read the small OTs were used to limit power so the speakers of the day wouldn't blow. The general idea is the smaller OT saturates, causes distortion, people didn't want distortion so they didn't turn them up so loud.
    If that's true or not I don't know. But in the 50's a Jensen P12N was about the highest wattage speaker Leo used and it cost alot more than the Q and R Jensens.
    Leo first used JBLs about 1959 in the Vibrosonic and it wasn't a cheap amp. Neither was the HPTT with two P12Ns.
    A little later on Dick Dale was blowing JBLs with Showmans. Speakers then really weren't that robust, compared to what we have now.
    Anyway if the small OT to save speakers theory is true or not I don't know. But if you look at the cost of speakers then and the wattage ratings it makes some sense.
     
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  8. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    [​IMG]

    That 250pfd cap is the treble tone cap, correct? IF that .1mfd cap off of the other side of that treble pot was increased to a .02mfd, I might think the midrange would really be affected??
     
  9. mRtINY

    mRtINY Tele-Afflicted

    May 7, 2015
    Orygun
    Well, if you look at the rest of the stack - that 250pF with part of the Treble pot bypasses the 100k+220k resistor. doubling the capacitance would shift the corner frequency down an octave...

    The 0.01uF cap is a shunt to ground. Doubling it would cut more midrange...
     
  10. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Thanks for that insight, mRtinY....
     
  11. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    That and cost - Leo "shaved" corners as music as possible to keep costs down. I built a 3x10 a few years ago and used a small OT - it works great in the studio as it saturates early and the volume is far lower than a Bassman.
     
  12. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    Leo gets a rap for cutting cost but compared to other amps of the same time, even Ampegs, which I love. His amps were better built hands down.
    He could've hard wired the speakers or left out the ext jack, he had RCA plugs for the footswitches and reverb. Just those little things would add up. Ampeg hard wired everything, saved time and money.
    The pro amps got the now controversial standby switch. Not really needed maybe but it's a switch and more wire, solder and time.
    Then if you want to compare Leo era Fenders (65 and older) to the cheap junk like Valco, Kay, Silvertone and so forth the differences are grater. Some of those literally had cardboard cabs compared to finger jointed pine.
    The output transformer in the "big" Silvertone 4-6L6 amp is about the size of the choke in most Fenders.
    I'm sure Leo saved were he could but he didn't build cheap junk.
    (OK he used a Champ PT in the Princetons)
     
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  13. peteb

    peteb Tele-Afflicted

    Apr 25, 2003
    Cascadia
    I also read the article about the smaller OT's meant for the low power speakers. It was a nice story, but not really substantiated.

    I agree, Fender did not cut corners.


    It appears fender used a range of OT sizes to expand the product line. there were a lot of tweed models. 2 single ended amps, the Princeton is supposed to have a bigger OT than the champ. Four 2x6v6 amps. Are all the OT's in the 2x6v6 amps on the smaller side? Isn't the 5e3 OT rated at lower than the output of the amp?
    There's nothing small about the OT in the holy grail amps, tweed twin and bassman
     
  14. screamin eagle

    screamin eagle Friend of Leo's

    Oct 9, 2008
    S. CA
    I certainly understand that, but I don't see being frugal as cheap. He respected the integrity of his product with respect to cost and business acumen.
     
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  15. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Well, Leo and Co. Did cut corners, ime. If not, they would have used P10N's in the tweed Bassman....and that still might have not been enough. They finally upgraded from P10R's to Q's in 1960.
    Here is a comparison of how Leo thought and say Rickenbacker did things. A Fender Champ ran the least expensive 8" speaker that could be found...whether it was Jensens in the '50's or Oxfords in the '60's.
    I have a 1964 Rickenbacker B9A....single 6V6 with trem....that not only has a 12" speaker but it is a Jensen C12Q. At the same time, Fender was using a lower capability 12" in the Deluxe Reverb!
    Yes, that copper chassis Ric sounds glorious through that C12Q....no need for a speaker upgrade.
    I have put a Jensen P8RS in a BF Champ, and it made the amp much bigger and richer.
    Leo watched the pennies...no doubt.
     
  16. telemnemonics

    telemnemonics Poster Extraordinaire

    Age:
    57
    Mar 2, 2010
    Maine
    Isn't there also an impedance difference between a dual 6v6 and a dual 6L6 OT, in addition to an expected size and capacity difference?

    Meaning that a BF Deluxe OT in a 5e7 would be impedance mismatched to the speaker?
    Or did the OP do the math and determine that the mismatch was corrected by presenting an 8 ohm single speaker load rather than the 3.2 ohm triple speaker load to the "wrong" OT?

    I would expect that a significant impedance mismatch would affect the sound, but I would not expect it to (combined with the smaller OT size) make an amp more punchy with increased headroom!
     
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  17. telemnemonics

    telemnemonics Poster Extraordinaire

    Age:
    57
    Mar 2, 2010
    Maine
    Re: Leo being cheap, frugal, etc; I have to wonder how we define "cheap" in terms of making a product that the target buyer can afford.
    If production costs are increased and the added cost is passed on the the buyer, as opposed to coming out of the manufacturers profit margin, wouldn't that be two different things?

    In a long storied history of bringing a fairly revolutionary product line to market, not a lot of clear "cheap choices" can be singled out over the two decades. A few undersized speakers and a transformer or two is maybe not a pattern of a "cheap manufacturer"?
    Compared to something like sticking blocks of pine in the ends of the amp chassis instead of folding and welding the corners?

    But a fairly expensive product line for a not traditionally wealthy buyer market, being successful in terms of the business staying afloat and the majority of customers being happy, it seems like overall good business decisions were made.
    Not cheap business decisions.
    I wonder how increasing the cost of most amps by using over rated speakers would have affected the market? Would buyers all happily pay more for the product? Would buyers simply buy the next cheaper amp?
    How much is our decision to buy a product today affected by the price?

    I wonder also what the expectation was for amps to be continuously run at full volume, vs an expectation that a buyer would choose an amp that produced the required volume clean.
    In terms of the average end user, would charging more for heavier speakers to allow the minority of buyers who ran undersized amps at full volume, rather than oversized amps at clean volume, make the best business sense?
    Or might the majority of buyers choose products that fit the application without being pushed to their limits?
    And might the majority of buyers choose to pay less for that product, rather than pay a higher price for heavier speakers that they did not intend to push to the ragged edge?

    Like when we buy an AC unit, do we buy one that's rated for a slightly smaller room, so it will run flat out? Or do we choose an AC that's a little big for the job so it will not be strained in the application?

    Just looking at the ethic of the time, or the ethic of product vs price.

    A well debated but still interesting topic...
     
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  18. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    Great point about the chassis not having wood blocks on the ends. Just that little detail added cost. The ends on the blackfaces were stamped, not just folded. Any sheet metal shop can bend a chassis. Stamping those ends ment making a die and having a pretty big machine. Of course back then shops like that were fairly common. Today not so much, that stuffs done over seas for the most part now.
     
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  19. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Superior Metalworking is down the road from me here in Tennessee and they have everything up to and including a mammoth 200 ton press. They make stuff for Kubota and Boeing among others.
     
  20. screamin eagle

    screamin eagle Friend of Leo's

    Oct 9, 2008
    S. CA
    I was at a buddy's house the other day who just got his old Magnatone up and running again. Not sure what model it is, but it's probably similar to a Varsity amp. One of their student models. 2x 6v6 with a 12" speaker and 6sn7 phase inverter. Not sure what the other preamp tube is, but it's a metal octal tube. Anyway the OT is about the size of a slot car motor. Seriously it is tiny. The amp has a great honking sax tone to it, but it has absolutely no bass at all.

    We recorded just some jams over a couple of tunes (Sweet Georgia Brown). He played his 295 through the Magnatone and I played a 335 through a 5D5 Pro.

    We traded comping and soloing.

    When I was comping the recording sounded full (for two guitars anyway), but when he was it was thin and reedy. While the 335 was brighter on the solo side of things (naturally), the was no bass at all coming from the Magnatone. We were competing frequency wise. When we'd switch back to me comping, the bass came back and the overall sound was balanced again.

    My point is this: smaller OT's restrict the lower frequencies. To some degree this can throttle back the boominess or gassiness of an amp and give it a singing quality, but too far (like this Magnatone) and you get an unbalanced sounding amp. This wouldn't matter if there was a bass--in fact it might make the amp track really nice in that tenor register without competing in the lower frequencies at all, but without a bass it's really lacking.
     
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