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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 5:02 pm
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Socal...if Retro, Shimmilou, BMW2002ti, Rebel Soul, and Aclempoppi give it the thumbs up and give you advice on a Vintage amp...take it for everything it is worth, these guys know their stuff and will walk you through just about anything. Retro was indespensible when I revamped my Bantam! These guys are walking encylopedias on Fender Amps!

Enjoy the amp, it is a Great score btw and welcome to the Vintage Fender Amp Club! :mrgreen:

T2

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 5:05 pm
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The "sizzling" like frying bacon sound could be a sign of instability. I'd try contact cleaner on the sockets. See if this helps.

Your amp has 2000 pico-farad caps attached to the 6L6GC (to ground). They are there as "after-thought" items to limit instability and "snub" high-frequency oscillations. They may have gotten toasted from use. Maybe a good idea to simply replace these.

Check the wiring around the sockets. Try keeping the lines as perpendicular to the socket tangs as possible. Are the solder point clean? Not cold looking or cracked?

The power tubes have two resistors soldered right onto the sockets. They are grid stoppers (1500 ohm) and screen resistors (470 ohm). Both are there to help limit instability and keep the 6L6GC happy. You may want to check to see if there is signs of damage or burnt bodies. If they are way out of spec (over 25%), I'd replace them with metal oxide, high-temp resistant resistors.

The reason I kinda latched onto the sizzling noise, is the "lower output" issue, too. Sometimes, instability and lower volume go hand-in-hand. Of course, it could be weak 6L6GC, too. Weak power tubes can have higher tendency to become unstable.

BTW... the Sovtek 12AX7LPS has sprial wound heater line like the old US made 12AX7A. I like the Sovteks. They aren't going to have the tone of a good NOS RCA or Raytheon. But, sound pretty good for a new made tube.


http://www.webphix.com/schematic%20heav ... ad1269.pdf


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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 5:23 pm
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BMW2002Ti wrote:
The "sizzling" like frying bacon sound could be a sign of instability. I'd try contact cleaner on the sockets. See if this helps.

Your amp has 2000 pico-farad caps attached to the 6L6GC (to ground). They are there as "after-thought" items to limit instability and "snub" high-frequency oscillations. They may have gotten toasted from use. Maybe a good idea to simply replace these.

Check the wiring around the sockets. Try keeping the lines as perpendicular to the socket tangs as possible. Are the solder point clean? Not cold looking or cracked?

The power tubes have two resistors soldered right onto the sockets. They are grid stoppers (1500 ohm) and screen resistors (470 ohm). Both are there to help limit instability and keep the 6L6GC happy. You may want to check to see if there is signs of damage or burnt bodies. If they are way out of spec (over 25%), I'd replace them with metal oxide, high-temp resistant resistors.

The reason I kinda latched onto the sizzling noise, is the "lower output" issue, too. Sometimes, instability and lower volume go hand-in-hand. Of course, it could be weak 6L6GC, too. Weak power tubes can have higher tendency to become unstable.

BTW... the Sovtek 12AX7LPS has sprial wound heater line like the old US made 12AX7A. I like the Sovteks. They aren't going to have the tone of a good NOS RCA or Raytheon. But, sound pretty good for a new made tube.


http://www.webphix.com/schematic%20heav ... ad1269.pdf


Those 2000 pf caps do look kind of toasty, hmmm. I think I'm gonna go ahead replace those and check the screen and grid resistors values. Thanks for the heads up.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 5:50 pm
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So Cal, Beemer is right on! IMHO A thorough cleaning of pots, jacks, and tube sockets would be a good idea. Retensioning the tube sockets would also be part of the clean-up. There are other possible sources of the sizzle, but I think you have enough on your plate for now. Art

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 8:25 pm
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Thanks Art, I definately have a full plate :D But i'm very excited to get this amp up to it's fullest potential.
On another note, the guy who sold me the amp told me the cab came with the original Utah speakers. Well I decided to remove the back cover to check it out and was a bit perplexed....Can anyone help me identify these speakers. I can't find any documentation on them and they look pretty "new" for being from a 73' cab????? By the way, they sound very nice and warm. I compared them to a 212 cab I have loaded with pre rola celestions g1280's from the 80's. The celestions have alot more top end and are more chimey. Although I actually like the sound of the ones in the cab as well. Only problem is I measure the resistance on the speakers and one reads 6.3 ohms and the other 6.6 ohms for a total impedance of about 3.4/5, at least that's what my meter was reading. I'm hoping this will not damage the O.T. over time since it's looking for 4 ohms.
Thanks again.
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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 10:02 pm
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So Cal, the other guys will take care of the codes. But I can give you the ohmage rule for speakers. Until a speaker exceeds the nominal designation, it is considered to be in the next lower category. Example: a speaker that measures between 4.1ohm and 8ohm is considered an 8ohm speaker. Example: 8.1ohm to 16ohm would be considered a 16ohm speaker. Example: 2.1ohm to 4ohm would be considered a 4ohm speaker. You know, maybe the Weber site has better info. HTH Art

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Thu Mar 22, 2012 10:36 pm
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aclempoppi wrote:
So Cal, the other guys will take care of the codes. But I can give you the ohmage rule for speakers. Until a speaker exceeds the nominal designation, it is considered to be in the next lower category. Example: a speaker that measures between 4.1ohm and 8ohm is considered an 8ohm speaker. Example: 8.1ohm to 16ohm would be considered a 16ohm speaker. Example: 2.1ohm to 4ohm would be considered a 4ohm speaker. You know, maybe the Weber site has better info. HTH Art


Correct.

Strictly speaking, a DCR impedance measurement does not precisely correlate to AC resistance. Thus, the 6+ ohms observed via meter measurement are consistent for a speaker with an 8-ohm voice coil.

As for the speakers themselves, it's impossible to determine what they are without the EIA codes that should be present somewhere on the frame or the magnet structure itself. They most certainly are not the OEM Utahs or OEM Oxfords which were both common to Bandmaster enclosures from this era (I own a '74). As well, four of the eight mounting studs have been removed from each speaker position -- it's possible that replacement Celestions were installed during at some point in this cab's existence. The wiring does appear to be factory-standard.

HTH

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Fri Mar 23, 2012 7:09 am
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Thank you both Art and Arjay. Let me remove the 30+ screws( :oops: ) and see if I can find the EIA codes. I think I can take it from there.

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Fri Mar 23, 2012 3:57 pm
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Well I found the speaker manufacturer, drumroll please......................eminence, lol. I just emailed them with this pic to see if they could give me more info such as type and wattage.
Thanks again to everyone who contributed to this post.
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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Fri Mar 23, 2012 4:21 pm
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Fourth week of 1978. Not certain what amp it belonged to but that "121496" looks like a bonafide Fender P/N. Possibly an ultra-linear Pro Reverb......?

Good job of sleuthing, socal.

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Sat Mar 24, 2012 3:18 pm
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Retroverbial wrote:
Fourth week of 1978. Not certain what amp it belonged to but that "121496" looks like a bonafide Fender P/N. Possibly an ultra-linear Pro Reverb......?

Good job of sleuthing, socal.

Arjay


Thanks Arjay, couln't have done it without the help of this forum.

Unfortunately I did a little more digging and found info on the eminence web site and it's actually from the 1st week of 2001, the A0478 is the serail number. So now I'm assuming its an Eminence speaker taken from a Fender "fill in the blank", 2001 model based on the fact that the part number is a fender part number. Still, a very descent sounding speaker.
Here's the link from eminence.
http://www.eminence.com/support/faq/

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Sat Mar 24, 2012 11:31 pm
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So if I'm not mistaken, the info tells us every thing but the wattage. It seems OK, to crank and pick, unless there is some other issue! So Cal, did I miss a beat on this groove? Art

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Sun Mar 25, 2012 12:37 am
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Do the cones have a slight purple or lavendar tint to them?

If so, they may be "pulls" harvested from a 4 x 12 Roc Pro cab. Around 80 watts RMS each, as I recollect. Thus, they'd fare well with a BMR head.

Arjay

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Tue Mar 27, 2012 10:13 am
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Art,
No, you haven't missed a beat. Its just difficult not knowing what it is that have. But we can put that to rest now.

Arjay,
I haven't taken a peek yet to see what color those cones might be but I did finally get a responce from eminence and it looks like you weren't far off at all.

Here's the info I received.

121496 was a custom designed OEM speaker that we manufactured to one of our customer's specifications. It is an 8 ohm speaker with a 1.75" voice coil and a 30 oz ceramic magnet. We do not rate OEM designs (that is left up to the customer to test and rate their cabinet or amp), but a conservative thermal power rating based on the voice coil diameter would be about 75 watts. Here are the T/S parameters:

05-RE OHMS 6.32 13-FS HZ 104.11 06-LE MH .61 14-MMS GMS 24.30 07-QM 9.66 15-CMS mm/N .0962 08-QE 1.000 16-RMS NS/M 1.6448 09-QT .900 17-VAS LTRS 36.47 10-XMAX MM .90 18-SD SCM 519.45 11-BL TM 10.03 19-EBP 104.4 12-EFF % 3.98 20-SPL dB 98.0

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Post subject: Re: Bandmaster reverb, my first vintage
Posted: Tue Mar 27, 2012 1:41 pm
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That's pretty considerate of them to respond with such detail. A lotta subcontractors won't give you the time of day even if you offer up a Rolex Submariner in exchange.

With a SPL of 98.0 dB they aren't real efficient but that'll let you flog the amp a bit harder to hit its "sweet spot". At 75 watts per, you've got ample power-handling capability.

Arjay

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