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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 4:01 pm
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Vinyl,

The Super, as you know, is an open back combo, the DUAL Showman runs into a Bandmaster cab with 2 EVM12L speakers. Depending on where the amps are located, pointed etc, the SR sounds "louder" but that might be due to reflections off the surrounding walls. I'll run a test with a SPL meter and report back.

Thanks again for the help on the DS Tremolo problems.

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 4:54 pm
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royb3988 wrote:
Vinyl,

The Super, as you know, is an open back combo, the DUAL Showman runs into a Bandmaster cab with 2 EVM12L speakers. Depending on where the amps are located, pointed etc, the SR sounds "louder" but that might be due to reflections off the surrounding walls. I'll run a test with a SPL meter and report back.


Correct.

Indoors, the combo usually has the edge in perceived volume because the rear-wave radiation from the speaker cone is audible as it bounces from wall to wall and ceiling to floor. But outdoors the bass-reflex enclosure projects all of its volume to the front (where an audience is typically seated). And the acoustic loading provided by the sealed back permits the speakers to be driven harder since cone excursion is controlled. A good example of this is Acoustic Control Corporation's 360/370 bass rig or the Sunn Coliseum with the 1-18H folded-horn cab. On stage they seem relatively quiet but thirty feet out from the bandstand they're ripping people's heads off.

Each cabinet has its own assets and liabilities. I usually play a combo but for outdoor venues I'll add a bass-reflex extension cabinet to cover any contingency.

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: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 5:07 pm
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Glad you've fixed the tremolo problem, hope you take the advice and have the electrolytics serviced to prevent potential failure in the future.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 7:14 pm
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Vinyl,

That sounds (pun intended) right to me, thanks!

sfceric64,

I will, thanks.

rb3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Sep 06, 2019 8:31 am
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Well...

My euphoria may have been too soon. I just turned the amp on, came off Standby after about 2 minutes, hit the foot switch...no Tremolo for 15 seconds, then it kicked in, but...the motor boating is still gone!

More later.

Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Sep 06, 2019 10:26 am
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sfceric64 wrote:
Glad you've fixed the tremolo problem, hope you take the advice and have the electrolytics serviced to prevent potential failure in the future.

RB,

Couldn't agree more with sfceric64 here.

The main enemy of electrolytic capacitors is temperature, time in service, something called ESR, and voltage rating.

While I'm in favor of not replacing components that aren't bad, once you have an amp apart, sometimes it makes sense to replace some parts that are likely to fail. Electrolytic capacitors fall into this category, as far as I'm concerned, because you end up replacing some components right away, and others in 3, 4, or 5 years. If you have the expertise to do this, then no biggie, but if you don't, then you're constantly running to an amp tech.

A perfect example of this is your amp. All of the plate resistors have apparently been replaced. Whoever took the amp to a tech complained probably of static (impulse) noise and that tech just replaced all of the plate resistors, rather than determine which resistor might be causing the problem because the time involved would be more than simply replacing all of them.

If you order the recommended capacitors, and take them to a competent tech, I don't think he will mind using your parts, and returning the parts he replaced. He will be glad to have your returning business for other problems.

How long would that extend the life of your Dual showman before needing service again? Hard to say, it depends on how many hours you play it everyday. Probably longer than 10 years.

You have a 52 year old amp, that is irreplaceable IMO. Don't skimp on servicing it if you can't do it yourself. There's no shame if you can't read a schematic.

That's my opinion FWIW.

Cheers,
vinyl


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Sep 06, 2019 10:55 am
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I took the Tung Sol 12AX7 from V3 and swapped it with a Mesa 12AX7...brand new, right out of the box...I had put in V2 the day before yesterday...motor boating returned. I took the Mesa out, put in a new Tung Sol in V3 and no motor boating. I'll let the amp cool sufficiently for a couple of hours and start it up again...more later.


RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Sep 06, 2019 1:29 pm
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RB,
Since you brought up tube replacement/swaps, the primary function of all those electrolytic capacitors is to regulate/supply each tube with sufficient voltage to operate efficiently. With a bad supply the tubes wont operate efficiently and may fail more often.
I will add, a bad tube is a bad tube to that.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Sep 06, 2019 7:34 pm
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Hello...

To test a resistor, does one end of it have to be disconnected from the circuit?


RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Sep 06, 2019 10:19 pm
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For a static DC resistance measurement, yes. You'll need to lift one leg of the resistor.

However, if you're familiar with the laws of Ohm and Kirchoff, the resistance can be determined dynamically without the need to isolate the component from the circuit.

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: Fender 1967 DUAL (in block letters) Showman
Posted: Sat Sep 07, 2019 10:41 am
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Arjay,

Ok, I might take the route of disconnecting one end, it's that 100k ohm resistor that ties to pin 8 of the V3 tube and the associated cap with it that have me wondering.

I'll follow up.

Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Sat Sep 07, 2019 12:20 pm
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Easy enough to lift one end (that's the beauty of an eyelet board).

Best to replace that resistor if is shows any significant value drift.

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: Fender 1967 DUAL (in block letters) Showman
Posted: Sun Sep 08, 2019 11:31 pm
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Team...

If I turn off my amp, leave the Standby switch in the up position, unplug it from the ac receptacle and then move the power switch to the on position for a minute or so, will that sufficiently drain any voltage or current from the amp making it safe to work on it?


Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Mon Sep 09, 2019 1:45 am
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You should be sure about residual voltage, before working on the amp. Unplug amp from wall outlet. Standby Switch to PLAY, POWER switch on. Let the amp sit for a minute or two.

Remove the "doghouse" cover over the main PSU caps. Measure the DC voltage from B+ side of caps to ground. See photo. Red lead of DVM onto B+. Black lead onto GROUND. Should be measuring millivolts (0.50 VDC or less). You are good to work on the amp, now. Be sure to turn POWER switch off and STANDBY to standby, before turning amp back on.

Good luck!

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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Mon Sep 09, 2019 6:18 pm
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BMW2002Ti,

Thanks for the info.

RB3988


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