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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 9:55 pm
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Vintage, a couple of questions: Is this amp stored near the beach? The bias circuit is a mix of cathode and fixed bias, can you check all components and wiring to the power tubes( especially V7)? To my eyes, it looks like the cathode resistor for V7 has been replaced. The carbon on the chassis seems to be in the area of the screen resistor, cathode resistor, and heater filament pins. But this also could have just been the weakest point. That socket must be cleaned of any carbon paths. And Yeah, all the Mallory caps need to be tested or replaced. The beach question has to do with salt air and calcification, rather than electrolyic fluid. This could very well be just a simple tube blow-out! But now you're stuck with the grunt work. Art

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sun Aug 26, 2012 11:35 am
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shimmilou wrote:
Again, the tube was likely broken while stored. It didn't pop when powered on. The white powder inside is evidence that the tube was powered on after breaking. Are you saying that it is impossible that someone else could have had access to the amp and moved it, or knocked it over?


Not a chance, I'm the Keeper of the Key (majority owner of the Studio) and no one goes in without me. I do all the equip set ups before testing and recording. We have a couple college interns that help set up, but I'm with them all the time. I've got too much vintage valuable Amps, Guitars, pedals and tech in the equip storage room to trust anyone else. We haven't' even had a decent earthquake around here to shake things in the last 5 years! Either that tube cracked during or immediately after "the event". I didn't look at the tubes till half hour later.


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sun Aug 26, 2012 3:05 pm
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The tube cracked. We know that. Where/when/how the tube cracked is irrelevant at this point. It is now time to troubleshoot the amp based on the advice provided. Good luck and let us know how it goes. :wink:

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sun Aug 26, 2012 7:21 pm
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bluesky636 wrote:
It does appear to be an AA768:

http://vintagefenderamprepair.com/wp-co ... ematic.pdf

http://vintagefenderamprepair.com/wp-co ... Layout.pdf

The 25/25 caps are for the preamp and reverb/tremolo tubes. I would definitely replace them. Once those are replaced, I would again recommend pulling all tubes (except the rectifier, of course) and checking the supply voltages. Then you could plug in the preamp/reverb/trem/PI tubes and check the voltages again. Finally, install the power tubes.

You might want to consider replacing the power supply caps as they all appear original. They don't appear to be physically leaking, but they should at least be tested and replaced if necessary.


BlueSky - the Power Caps were replaced once, think it was about '97, the tech I used up in LA had a stash of hundreds of original NOS caps, tubes, resistors, etc he bought off Fender, some kind of garage sale in the mid 80's, think it was after the CBS sale. This BMR had two leaky power caps he showed me. I think that's why they look original.

After I discharge the Preamp section and power tube section Caps, I'll figure out how to check their values and see if they are out of spec. While I'm at it I'll check the values on all the other small components around the power section.

shimmilou - Still puzzled about those preamp section Caps. After you mentioned caps don't leak "uphill", I had that "DUH" moment, guess I was thinking upside down (chassis in the cab). No, it wasn't stored on it's "head". BUT what is that fluid Residue on those two caps? They're too far away from the solder points to be solder Flux. Is that any kind of indication of a problem with them?

Someone asked if it's stored near the beach? Nope, I wish we had a beach side studio but not with the money we make these days in the music industry in Calif. :(

Will start diving into sorting out values after discharging all of the caps. may have a few questions as I test things, guys. So please keep an ear on the tracks for shouts for help. Thanks for the advice.

One last Question/Advice (poll) from the sound Experts - Aside from vintage NOS Power Tubes, Rectifiers and Preamp/Trem tubes, what is your favorite reliable good sounding "budget" tube brands for old (pre 90's) Fender amps?


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sun Aug 26, 2012 7:37 pm
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vintageguitarz wrote:
One last Question/Advice (poll) from the sound Experts - Aside from vintage NOS Power Tubes, Rectifiers and Preamp/Trem tubes, what is your favorite reliable good sounding "budget" tube brands for old (pre 90's) Fender amps?


JJs from http://www.eurotubes.com/

NOS from https://www.kcanostubes.com/

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Tue Aug 28, 2012 2:53 am
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Yeah Vintage, I was just taking the outside chance of salt air-moisture(lived on boats). If the cap only has a small amount of leakage, it can wick upward. Unusual, but I've seen it with the brown syrup evidence. At any rate, the caps are candidates for replacement. The power caps are your call. Art

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Post subject: Re: My '68 Bandmaster Reverb blowing fuse, Caps /TUBES choic
Posted: Tue Aug 28, 2012 8:59 am
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aclempoppi wrote:
Yeah Vintage, I was just taking the outside chance of salt air-moisture(lived on boats). If the cap only has a small amount of leakage, it can wick upward. Unusual, but I've seen it with the brown syrup evidence. At any rate, the caps are candidates for replacement. The power caps are your call. Art


I think I will replace them, ultimately since the preamp section is obviously important to the sound quality.

Any suggestions on where to find very good OEM or NOS caps at a low price?

Also still looking for suggestions on good quality tubes by brand, that all you guys believe in for reliability and sound quality, but are budget minded?? I've heard JJ's are good for preamp, maybe power, but read numerous complaints online about their rectifiers and some power tubes going south too fast. I know I'm staying away from Chinese tubes. How about Russian tubes and which?


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Tue Aug 28, 2012 12:04 pm
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I've had pretty good luck with the EHX power tubes (both 6L6 and 6V6). They're reasonably priced, sound good, and seem to last. I believe they're made by SovTek.

Arjay

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Tue Aug 28, 2012 1:31 pm
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Anyone had any experience with the new SovTek 6L6WXT+ in vintage Fender Amps??.
They are claim that they are "Modeled after the vintage RCA 6L6GC "Blackplate"". Price is $30 for a matched pair.

Old USA GE 6L6GC's are, er WERE in the '68 BMR. (one cracked in the arcing episode).

BTW - found this interesting debate on another forum about love or hate SovTeks, JJ's and other re-brands and who actually makes who. The thread is from 2010, and unfortunately doesn't help me a lick deciding what to buy for the BMR :? But it's fun to read.
Love em / hate em! - http://www.tdpri.com/forum/bad-dog-cafe/192847-any-opinions-sovtek-tubes.html#post2230766
Who makes who? - http://www.tdpri.com/forum/2230766-post21.html


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Tue Aug 28, 2012 3:58 pm
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Like I said earlier, I like JJs from Eurotubes and I know where they come from:

http://www.jj-electronic.com/

I am using their preamp (12AX7), power tubes (6L6GC and 6V6S), and rectifier (GZ34/5AR4) in my amps with no complaints.

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Tue Aug 28, 2012 8:08 pm
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bluesky636 wrote:
Like I said earlier, I like JJs from Eurotubes and I know where they come from:
http://www.jj-electronic.com/
I am using their preamp (12AX7), power tubes (6L6GC and 6V6S), and rectifier (GZ34/5AR4) in my amps with no complaints.


BlueSky, might I ask what amps / models have you've used them in?

As you can imagine, opinions on any particular brand and even which brand with what amps are pretty plentiful on all the sites I've been looking at.

One problem I'm going to encounter with this 68 BSM is that there is no Bias adjustment, only a Bias Balance (pot). So I need to find the best brand match for a late 60's /early 70's Fender Silver Face. I'm not interested in doing a conversion to a Bias Adj circuit, just get it too reliable and good sounding so I can sell it with a good conscience to someone.


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Tue Aug 28, 2012 8:44 pm
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vintageguitarz wrote:
bluesky636 wrote:
Like I said earlier, I like JJs from Eurotubes and I know where they come from:
http://www.jj-electronic.com/
I am using their preamp (12AX7), power tubes (6L6GC and 6V6S), and rectifier (GZ34/5AR4) in my amps with no complaints.


BlueSky, might I ask what amps / models have you've used them in?

As you can imagine, opinions on any particular brand and even which brand with what amps are pretty plentiful on all the sites I've been looking at.

One problem I'm going to encounter with this 68 BSM is that there is no Bias adjustment, only a Bias Balance (pot). So I need to find the best brand match for a late 60's /early 70's Fender Silver Face. I'm not interested in doing a conversion to a Bias Adj circuit, just get it too reliable and good sounding so I can sell it with a good conscience to someone.


Fender Champion 600 (converted to 5F1 Champ configuration): JJ 12AX7, JJ 6V6S

Fender Blues Deluxe Reissue: V1 - NOS JAN GE 12AY7, V2 - JJ 12AX7, V3 JJ 12AX7, V4/5 - JJ 6L6GC

Weber 5F6A Bassman Clone: V1 - NOS JAN GE 12AY7, V2 - JJ 12AX7, V3 JJ 12AX7, V4/5 - JJ 6L6GC

I buy the JJs from http://www.eurotubes.com. Give them a call and talk to Bob. He will help you find the best tubes for your amp.

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Post subject: Re: Bias Testers - My '68 Bandmaster Reverb GZ34 is Arcing!
Posted: Wed Sep 05, 2012 12:21 pm
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An update guys -

I'm not finding anything in the circuit that appears to be the cause of the Rectifier arcing and the Power Tube #2 doing a swan dive to a sudden blow out. But I continue to look and measure.

In the mean time I've ordered two new matched Sovtek 6L6WXT+ Power Tubes and a new JJ GZ34 / 5AR4 Rectifier tube (I found the absolute best prices at Tube Depot after a lot of online research).

I need some opinions on a Bias Tester I've been looking at. This seems to be the best deal around for a "Dual Tube" Bias Tester accessory which also allows plate voltage output (I already have a very high end Fluke DMM clone made by Samsung). Do any of you have experience with the "Dual BiasTester-MPD™" http://www.amp-head.com/product_info.php?cPath=21&products_id=70. The price is $85. which seems VERY reasonable.

Any other suggestions for a tight budget? Appreciate the feedback and advice.


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Wed Sep 05, 2012 6:35 pm
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Yes, I'm a broken record. There is virtually no way that any problem in the amp could cause an output tube to crack its glass instantly upon power up. A broken output tube however, definitely could cause the rectifier to arc and the input fuse to blow.

This is why it's important to know when the tube glass broke. Whether it is a cause or a symptom is of the utmost importance to know what actually happened to your amp. Whether it was broken when the amp was put away, while it was stored, or when it was removed from storage, it seems very clear to me that it was indeed broken not as a result of an amp problem, but as a result of a physical blow to the amp or directly to the tube itself.

I predict that replacing the output tubes, rectifier tube, and a proper bias/balance setup is all that is needed to return your amp to operating condition. The rectifier tube might be fine, but a good idea to replace it since it was hammered and arced.

And, be sure that you replaced the blown fuse with the proper 2 amp slo blo rated fuse.

I know some members here use the probe in your link. I use and recommend this one.
Quadstage BiasPro MQ10 - http://www.asharpfretworks.com/5543.html
You can get 8-pin probes, nine pin probes, and Plate voltage probes, and check up to four tubes at once. I measure Plate voltage with a meter, so I don't need an additional voltage probe.

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Wed Sep 05, 2012 8:00 pm
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Shimmy,

I have some issues with pin diameter of certain JJ and Sovtek power tubes and rectifiers. Either too emall or worse, too big, for old US made sockets. Where the tube has to be forced into the socket. I've seen a couple cracked output & rectifier tubes, at the base of the tube (seams, exp).

Or broken pins and sockets:


http://www.timeelect.com/pins-2.jpg


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