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Post subject: Output transformer mystery.
Posted: Thu Apr 11, 2019 4:42 am
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Hi. I am hoping that someone can shed some light on whether my situation is common or not...i have a 61 Bandmaster w tone ring cabinet (ie one 12 inch speaker) but the output transformer is a 45216, which I believe is intended for a 4 ohm load (2 12s in parallel). The date codes on all the transformers, pots etc indicate latter half of '61 so I believe that it is the original OT. I have had the amp since the early 70sand it hasn't blown yet. Did this happen often?


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Post subject: Re: Output transformer mystery.
Posted: Sat Apr 13, 2019 12:15 am
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My information indicates that P/N 45216 is an output tranny for a 6G4 Super Amp.

The correct P/N for a blonde Bandmaster O/T would be 45217.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Output transformer mystery.
Posted: Sat Apr 13, 2019 3:10 am
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I agree. So that's the mystery. According to the schematic the amp is a 6G7A and the OT should be a 45217. The blonde blonde BM 6G7A was sold in 61 with a single 12 (8ohm) cabinet and then in 62 with a 2 x 12 cabinet (4 ohm). Although it stands to reason that they would use different OTs for the different cabinets I have only ever seen a schematic showing the 45217 for the 6G7A circuit. To further confuse the issue the schematic shows one speaker and no extra spkr jack but the chassis layout diagram (and my amp) show the extra jack. So I guess my question was is it more likely that they accidentally used the wrong OT in my amp or is it possible that the head was intended to be sold with a 2x12(4 ohm) cabinet? The date codes on all 3 transformers are within weeks of each other (mid 1961) so I am still thinking that its original.


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Post subject: Re: Output transformer mystery.
Posted: Sat Apr 13, 2019 3:52 am
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Quetico wrote:
...or is it possible that the head was intended to be sold with a 2x12(4 ohm) cabinet?


That *might* be the most logical scenario.

The single-twelve tone-ring cab was replaced by the more familiar 2 x 12 layout but the plant may have run out of the new tranny (with its four-ohm secondary) so the Super Amp O/T (with very similar performance specs) was substituted. Or the Bandmaster's original tranny failed very early and a tech used whatever happened to be on hand to return the amp to service. Plate voltages are similar for the two amps (456 VDC for the BM, 448 VDC for the Super), plate-to-plate impedance is around 6KΩ, and the 4Ω secondary is consistent for an amp driving a pair of 8Ω speakers wired in parallel.

It's a mystery for sure but honestly, it isn't anything that would cause me to lose sleep.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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