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Post subject: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 10:01 am
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https://1drv.ms/i/s!Ai3hnpDg_gL8gb11tew8LQg6q_BxTA

Apologies if this is a silly question, but looking at this Bandmaster head last night I couldn't figure out what this red cap between the fuse and the power switch is. The amp has an oddball long toggle switch for the power as opposed to the short switches for the standby and ground but the wiring to it looks original. The death cap is off to the side as per normal, and it still has its original 2 prong plug.
Any ideas from the experts?? Also, does anyone have any ideas how to get a stuck fuse holder cap out?

Thanks in advance everyone for any info and advice. : )


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 10:14 am
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I would say to help stop the arcing (pop) when it's switched off but that's usually done on the stby switch.

UN


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 11:04 am
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upnorth2 wrote:
I would say to help stop the arcing (pop) when it's switched off but that's usually done on the stby switch.


+1

It's not shown on any Bandmaster schematic and it's nothing I've ever encountered before.

Arjay

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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 11:20 am
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Thanks guys!
When I got the amp there was a replacement output transformer, so I figured there might be a few more repairs in the amp. The more I look at the amp, it appears that is otherwise 100% original.
And if Arjay has never seen this it must be odd, lol. Just another reminder these amps were hand made and exceptions did sometimes occur. As much as the odd shaped toggle switch bugs my ocd, I think I will leave this one alone and just worry about putting in a 3 prong plug.


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 12:22 pm
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I've owned a half dozen or so Bandmasters over the years and currently have three -- two AB763's and one AB768. That cap is definitely an afterthought added by a previous owner. The correct O/T for a Bandmaster will be marked with Fender P/N "125A6A" (FEIC) or "022848" (FMI). If the latter, it may have been made by Better Coil & Transformer, with an EIA code of "831XXXX". The more common Schumacher tranny will be stamped "606-XXX".

Arjay

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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 1:38 pm
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That cap is really strange. I might just yank everything out when I do the three prong plug, and put in a short toggle switch to match the schematic. The fuse holder is not cooperating right now either. More items on the to do list. : )

Someone had put in a Dynaco A70 output transformer at some point in its life, I guess trying to do the "Bassman" mod. Those transformers were not designed to hang upside down ever. I have already put in a Classic Tone o/t to ease the strain on the chassis, but haven't got at anything else since school started last year. I had time to open it up the other night and have a really good look at the chassis. Mostly needs a recap, and a solid cleaning. : ) Still sounds fantastic as is. I am hoping to work on a couple of amps before school hits in September. : )


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 5:42 pm
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Hokusai22 wrote:
Someone had put in a Dynaco A70 output transformer at some point in its life, I guess trying to do the "Bassman" mod.


Did the amp arrive with EL34's installed in lieu of the 6L6GC's? That tranny can probably drive either type since their plate-to-plate impedance is very similar.

Arjay

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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 03, 2017 5:47 pm
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Most arc suppressing networks I've seen across a switch involve a cap AND resistor. Exact values depends on current and voltage involved.

https://i.stack.imgur.com/kipGx.jpg


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sun Jun 04, 2017 2:49 am
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Hokusai22 wrote:
As much as the odd shaped toggle switch bugs my ocd, I think I will leave this one alone and just worry about putting in a 3 prong plug.


I'm wondering if that bogus replacement switch is of the correct voltage and amperage specs. That *might* be the reason for the oddball cap.

Arjay

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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sun Jun 04, 2017 7:32 am
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Retroverbial wrote:

+1

It's not shown on any Bandmaster schematic and it's nothing I've ever encountered before.

Arjay


Not original , it is a mod IMO


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 10, 2017 6:15 pm
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So, when in doubt return to spec. I have ordered the parts to put her back to normal. And, Arjay the amp arrived with cheap tubes, so Sovtek 6L6, EHX 12AX7 etc. It was definitely in player condition when I got it, but it was really cheap. : ) I have a cab to convert it into a 1x12 combo at some point, probably running a Celestion Type A speaker.

Thanks again guys!


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sat Jun 10, 2017 8:32 pm
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If you expect the full 40-watt output from the amp, that single twelve should be of 4-ohm impedance. With an 8Ω speaker, the amp will only develop about 28 watts.

Arjay

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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sun Jun 11, 2017 7:01 am
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Retroverbial wrote:
If you expect the full 40-watt output from the amp, that single twelve should be of 4-ohm impedance. With an 8Ω speaker, the amp will only develop about 28 watts.

Arjay


Absolutely. When being "nice" to transformers, the end result suffers. Just like discipline when it comes to children.

UN


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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sun Jun 11, 2017 7:41 am
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The "suffering" isn't as bad as it might seem since Leo's trannies back then were over-built to withstand such scenarios. There will be some inherent distortion caused by the mismatch but many find that sonically pleasing. Otherwise, there is no danger to the amp.

Arjay

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Post subject: Re: 67 Bandmaster head - mystery cap
Posted: Sun Jun 11, 2017 10:31 am
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Where I was going with that Arjay, I thought it was easier on a 4 ohm OT to run an 8 ohm speaker than the recommended 4 ohm speaker. I could be wrong on that.

UN


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