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Post subject: Bandmaster reverb, my first vintage
Posted: Wed Mar 21, 2012 8:51 pm
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I just got my hands on my first "vintage" amp. It's what appears to be a 72' Bandmaster Reverb. I'ts got one RCA 6l6 and one GE 6l6, 7025's x3, 12at7 x2, and one 12ax7. All appear to be either rca's and or vintage. I want to overhaul the amp and would like to get some feedback before I start. These are the questions I have:
1. Should I replace all the Paktron caps with equivelant value orange drops? (715 or 716's)
2. I looks as if all the filter caps have been replaced with xicon electrolytics. How much of a difference would it make if I opted for F&T's? Also, schematic calls for 70uf 350V x2 and 22uf 450V x3 but they installed 100uf in place of the 70uf. What effect does that have if any?
3. Should I retube and save the current tubes?
4. Any other suggestions?
Here's a link to some pics I took.
http://photobucket.com/bandmasterreverb
Thanks,
Abe.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Wed Mar 21, 2012 10:30 pm
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Before I begin, the vintage amp owner's creed bears repeating......

FIRST......DO NO HARM.

You've done a fine job ascertaining and documenting the condition of the amp -- kudos.

As for the enumerated issues:

Leave the Paktrons in situ -- they're much better-sounding than Orange Drops by a wide country mile.

The Xicon's are good electrolytics and the re-cap appears to be relatively recent -- I'd leave them alone for the time being. As for the value change, the 100uF cap will likely tighten up the amp's bass response a skosh. That can be good or bad, depending upon a number of other variables. If the amp sounds good, I wouldn't pay the difference any mind.

Unless one or more of the existing tubes are marginal (low transconductance or microphonic) I'd use them. They won't last forever, even in a stored condition. Better to get the last full measure from them lest they expire before you can enjoy them. I would recommend an idle-bias check and -- if necessary -- an adjustment. While you're at it, check the phase inverter (V6) for balanced transconductance between the sections. Replace if appropriate with a quality 12AT7.

The only other detail is that of safety. If it hasn't already been done, install a grounded 3-conductor power cord and disable the "death cap".

The BMR shares most of its chassis architecture with the Super Reverb -- thus, a number of sonic options are possible depending upon what size and type of speaker(s) you decide on. Bear in mind, the output tranny will perform at its best with a 4-ohm load.

Congrats on a great score, HTH

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 12:12 am
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Totally agree with Retro. I've had amps, on my bench, with RCA and GE power tubes,in unison that are a great match. I wouldn't mess with a thing, at this point. Check the bias, if you're concerned. Art

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 1:41 am
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+1

The beauty of the BMR is, it can be cloned into one of two very tasty amps. Dropped into a 4 x 10 combo cab with a quartet of 16-ohm Weber 10A125's and it becomes a Super Reverb. With only a bit more work a passable 1 x 15 Vibroverb is the result. I've also seen them configured as 2 x 10 combos, complete with blonde/wheatstraw cabs and blackface front panels......very cool.

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 6:40 am
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I can add only this...I totally agree with Arjay's opinion on Orange Drop caps....they lack the character that I want to hear,to my ears they seem unnaturally bright and sterile...but that's me.
ymmv as usual.
Congrats on a great amp!


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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 9:48 am
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Nice amp socal323! And thanks for the excellent pics. No pic of the outside?

Retroverbial ----> excellent advice!

Did anyone notice the EIA date codes on the transformers? A perfect example of how they can sometimes be difficult to decipher, and aren't always consistent. Usually, the year is the first part of the code (one or two numbers), and the week is the second part (two numbers), for both three and four digit codes.

The power trans has a 4-digit date code with the week first (50), and the year second (72),

The output trans also has a 4-digit date code with the week first (06) and the year second (73),

The reverb trans has a 3-digit date code with the year first (3) and the week second (05).

Looks like the codes on two of the trans, date this amp to early '73, with power trans made in late '72.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 10:53 am
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Nice catch! As Arjay said, don't do any change-outs without a good reason. Way out-of-spec coupling caps (esp if they are leaking DC) would be the a good criteria. Wholesale change-outs is a bad criteria. You may change out all the caps and not like the tone. Then, what do you do? Put all the original ones back in? Half of them? Only the ones around the input tube or phase inverter?

Many folks get into this trouble. Where they start changing things out, don't like the results. But then can't get back to a where they like the tone. Play the amp, as is. As long as the bias is stable, the amp isn't a hum monster. Or things go "poof" in the night. You are prolly cool. And it takes awhile for you to get the settings dialed in on the amp and the guitars. Good to give both you and the amp a break-in period.

The 100mfd/350VDC (or 450VDC) cap is used because I'm not aware of any quality, newly made 70mfd/350VDC 'lytic available on the market. And the total capacitance of the two 70mfd/350VDC networked caps is 35mfd/700VDC. The total for the 100mfd/350VDC is 50mfd/700VDC. Not a big difference. F&T now has 80mfd/450VDC caps, FWIW.

What you may want to do is use a little contact cleaner (I like Deoxit GN5) on the sockets. tube pins, jacks, reverb signal wire plugs, speaker plugs. Just a little for each contact and work the stuff by inserting and removing plugs and tubes a couple of times. This will make for a good contact on metal parts which maybe a bit oxidized or have little dingle berries on the surfaces. If the control are scratchy, a little spritz of cleaner usually clears up the noise.

Enjoy the amp. Maybe after a few test drives, then post what you think of the tone.

I redid a SF BMR head unit into a 2 X 10-inch combo. Dang thing is one potent little beast. I just changed out the 'lytics (they were original). And put in some 1990's era Svetlana SV-6L6GC. One LOUD puppy for sure. Good stuff!


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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:17 pm
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A huge thanks to all for all your input. Alot of good advice.

I noticed that it already has the 3-conductor power cord installed, hopefully that means that the "death cap" has alread been removed. But i'mma gonna double check.

Sounds like I've got a bit of homework to do, how to bias the amp and how to check for balanced transconductance between the sections. I've biased other amps so i have an understanding just not for this particular amp.

I noticed that for a 40 watt amp it's not as loud as my 40watt pignose. I'm familiar with what 40 tube watts should sound like and it's not happening hear, not yet anyways, so maybe it is in need of new tubes and screen grid resistors. I'm also hearing a bit of a sizzle sound, kind of like a bee buzzing in the background. Any ideas? Is that pot in the chasis a hum balance pot or a bias pot? On the schematic it looks like a balance pot.

Oh and one more thing, are 12ax7's suitable replacements for the 7025's without any modifications? I really dig the sovtek 12ax7lps and the tungsol RI 12ax7's.



Thanks again,
Abe

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:31 pm
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Your 7025's may be replaced by a high-quality 12AX7A. The 7025 was a low-noise military/industrial equivalent to the original 12AX7, developed for use in critical applications such as airborne transmitters or commercial broadcasting equipment. The resulting improved signal-to-noise ratio was achieved by slightly reconfiguring the elements within the glass envelope. The 12AX7A will accomplish the same task.

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:32 pm
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[quote="shimmilou"]Nice amp socal323! And thanks for the excellent pics. No pic of the outside?

Just got around to it now, I uploaded a couple to the same album. Definately have to redo the grill cloth. But at least the cab was loaded with the original Utah's, don't know if that's a good thing or a bad thing yet.....

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Last edited by socal323 on Thu Mar 22, 2012 4:36 pm, edited 1 time in total.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:33 pm
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Retroverbial wrote:
Your 7025's may be replaced by a high-quality 12AX7A. The 7025 was a low-noise military/industrial equivalent to the original 12AX7, developed for use in critical applications such as airborne transmitters or commercial broadcasting equipment. The resulting improved signal-to-noise ratio was achieved by slightly reconfiguring the elements within the glass envelope. The 12AX7A will accomplish the same task.

Arjay


WooooWhooooo, thanks Arjay.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:35 pm
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If you cut-and-paste the "IMG code" for the file within a post, your pic will appear thus......

Image

HTH

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:38 pm
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Retroverbial wrote:
If you cut-and-paste the "IMG code" for the file within a post, your pic will appear thus......

Image

HTH

Arjay


Nice tip, thanks again.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:52 pm
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If/when you decide to re-grill that speaker cab, do not discard the original cloth. From the looks of it, there's likely enough usable area remaining to restore a couple of smaller silverface combos.

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 4:56 pm
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Retroverbial wrote:
If/when you decide to re-grill that speaker cab, do not discard the original cloth. From the looks of it, there's likely enough usable area remaining to restore a couple of smaller silverface combos.

Arjay


Good observation, I'll keep that in mind.

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