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Post subject: 1970 BMR project..
Posted: Thu Aug 18, 2011 10:48 am
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Roadie
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Doing a BMR to a Vibroverb type of thing. Project pretty much done but I noticed that reverb doesn't have too much adjust ment. At 2 its kind of there and at 3 its over the top. I do remember reading about this somewhere I just couldnt find it again. It has the standard 100k L pot and no other mods. Is there a fix or a mod for this to get more out of the pot. Thanks....


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Post subject: Re: 1970 BMR project..
Posted: Thu Aug 18, 2011 10:57 am
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What kind of shape are your driver (V3) and recovery (V4) tubes in?

Arjay

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Post subject: Re: 1970 BMR project..
Posted: Fri Aug 19, 2011 9:43 am
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I have swapped out a few dif tubes. But those were older ANOS tubes. I will put a couple new modern tubes in there for troubleshooting.


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Post subject: Re: 1970 BMR project..
Posted: Fri Aug 19, 2011 3:23 pm
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If that is unsuccessful, carefully disassemble and inspect the reverb tank itself for any damage or anomalies.

HTH

Arjay

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Post subject: Re: 1970 BMR project..
Posted: Fri Aug 19, 2011 8:10 pm
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Sorry to interject... you may want to also measure the voltages on the anodes and across cathodes-to-ground on the 12AT7 driver and 12AX7 (7025) recovery tube for the reverb stage. If they are in range (+/- 15% of nominal voltage on schematic) and the reverb tank seems ok... maybe try a logarthmic pot (audio taper) in place of that 100-k-ohm linear taper pot?

On a few amps... I've seen too sensitive pots and all voltages, resistors, and caps around it seem ok, I've gone to audio taper with some success. Very common in newly made audio amps--- where they try to avoid using log taper pots.

I presume you reverted to the classic AA964 circuit:

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


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Post subject: Re: 1970 BMR project..
Posted: Mon Aug 22, 2011 5:53 am
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thanks for the hints guys. Much appreciated. I used the Vibroverb AB763 print to work off of to get the BMR into virboclone territory. I must say with the bigger OT from Allen Amps and the Altec 15 the amp has great punch and balls. What I didnt mention was I did atotal rewire to all cloth covered wire. Not neccessary but I felt like. With that the chassis is much neater. I may go the route of a different style pot after digging in a bit more with the suggestions here.


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Post subject: Re: 1970 BMR project..
Posted: Mon Aug 22, 2011 9:35 am
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How about some pics?

8)

Arjay

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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 5:56 am
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Retroverbial wrote:
How about some pics?

8)

Arjay


sorry....I have a bunch of "in the process" pics but no completed ones up yet. I will post them soon though. With BMR I kept the faceplate and aged the grill cloth and added trim to match the 68 style which I dig. I had a cab made by JD Newell which currently houses a single 15 altec. Have Winged C 6L6GCs and assorted RCA and other nice pre amp tubes in the mix. The recto is a ANOS Mullard GZ 34...... Minor tweaks in the tone stacks and a mix of Mallory 150's, Atoms, ODs, Silver micas, FT (filters) that round out the cap changes.
Did the tremelo mod which removes it from the circuit. Thats proving to be a nice mod with the 15 inch speaker set up. Gives it a bit more top end without being harsh at all.


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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 2:21 pm
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"In-progress" pics are always useful too -- how about putting them up?

Arjay

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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 3:37 pm
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Retroverbial wrote:
"In-progress" pics are always useful too -- how about putting them up?

Arjay


OK...you asked for it. Plenty to go through..... :roll:

http://gitarmoto.shutterfly.com/236

http://gitarmoto.shutterfly.com/292


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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 4:09 pm
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Pretty clean......it doesn't look like any "molestation" ever occurred. AA270 revision, judging by the biasing arrangement and the type of lead-dress.

Sweet!

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: 1970 BMR project..
Posted: Wed Aug 24, 2011 7:26 pm
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Roadie
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Thanks Arjay.....
The amp is a 1970 and it was never really touched and pretty clean. Typical of that time the wiring was pvc and a bit messy. Thats why I rewired with cloth and tried to get the layout more like the AB763 schem. I really dig the sound of the single 15 matched with what's running in the circuit right now. I had a 2x10 baffle cut for the cab as well. Currently having two Jensen P10PFs being reconed by Weber to P10N specs. So I can check that config out as well.


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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 7:48 pm
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You're making me antsy to get my newest amp project onto the front burner!

8)

Arjay

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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 8:00 pm
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thats what happens to me. I dont do anything for a while then I go for something after I see stuuf on this forum and others too. . Almost went for 69 Vibrolux on ebay today. Was in need of a decent amount of TLC. Had totally stripped down and poorly stained cab with a black grill. But the chassis looked in tact. Sold for 520.00. Not too bad of a price.....


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Post subject: Re: 1970 BMR project..
Posted: Wed Aug 24, 2011 8:07 pm
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Not bad at all!

Most VLR's go for three times that.

Arjay

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