Fender Custom Shop Rumble Bass Head 300w all Valve.

[Nostromo]

Hi,

I’m looking to find a good valve amp repair person in the UK to undertake what I suspect will be extensive repairs on my cherished Custom Shop RumbleBass head.

My RumbleBass is suffering from overheating/breakdown problems (which I'm told are due to poor chassis ventilation) that regularly afflict this model. I’m told the issues are partly due to shortcomings in the amps original ventilation design coupled to the use of cheap low quality components, and that ALL RumbleBass Heads have the same issues, and because of the problems with this rare model there are hardly any RumbleBass heads left in working condition. I’m therefore all the more determined to keep my example up and running - if I can find someone able to undertake the required work ?

So far, three different techs have looked at the RumbleBass but none have been able to affect a repair. One repair guy kindly looked at the amp for free - he didn’t charge me as he couldn't get to the bottom of the problem. Since then I've been to two other techs who have between them recommended complete replacement of all the pre amp and power valves and undertaken lots of biasing adjustments but none of these repairs or adjustments have lasted more than a couple of hours until motor-boating noises, crackling & popping noises, and intermittent volume loss returns. Such a shame because when working properly this amp sounds amazingly good.

Since then I've been told that valves are not the problem at all and that these repairers have been looking at the wrong thing ? . . . .

Psycho Bass Guy who is a regular contributor to the "Vintage Amps Bulletin Board" appears to be extremely knowledgeable on these amps, (unfortunately he's not in the UK) and he advises me that my Rumble Bass head probably needs a complete recap, including the small coupling caps, and probably could do to have all the critical resistors changed, too. Also, both the Pre Amp and Power Amp Chassis units will both needs to be modified to include some physical ventilation to improve heat dissipation. Unless this chassis modification is undertaken I’m advised by Psycho Bass Guy that the overheating problems will quickly return – unless, as someone else has suggested, I can find new componentry that can withstand higher temperatures than the original components.

A couple of people have said that these amps were fitted out with surprisingly low quality budget componentry, considering they were top of the range custom shop models when new, and that this fact doesn’t help. I have no understanding as to whether it would be possible to specifically select replacement components of higher quality/reliability that are designed for higher temperatures ? I would want to keep the electical properties/values of new components the same so as not to change the tone of the Amp ?

Obviously with such a rare and valuable Custom Shop Head I don’t intend to start drilling cooling holes in the chassis units if there is any other way ahead possible ? . . . I maintain the secondary objective of keeping the amp as close to original as is possible, though my priority is that I do want it to be reliable and usable and I dont want to introduce any components that would change the tone of the amp, which I love as it is.

In the first instance I need to find someone expert enough to diagnose the amp properly, identify appropriate replacement components, recommend a way ahead and undertake the required work ? . . So any recommendations on a good amp repair tech in the UK very very much appreciated.

Thanks,

Nostromo

[voxpop]

I have used this guy to service my vox valve amp..... Www.stevesamps.co.uk

Edited March 13, 2011 by voxpop

[MarkBassChat]

[quote name='Nostromo' post='1160421' date='Mar 13 2011, 04:07 PM']Psycho Bass Guy who is a regular contributor to the "Vintage Amps Bulletin Board" appears to be extremely knowledgeable on these amps, (unfortunately he's not in the UK) and he advises me that my Rumble Bass head probably needs a complete recap, including the small coupling caps, and probably could do to have all the critical resistors changed, too.[/quote]I don't think that this is a good advise. It is possible that some caps need to be replaced but I never do it, or advise other people do it, if I don't know the exact reason of the problems. When you have a problem with a car, you do not start replacing all parts, but you look for the source of problems. Exactly the same is with amps. Usually, problem is caused by a few components and you should first find out which components need to be replaced. Replacing everything is the worst possible advice you can give to someone. Your problems look like related to cold soldering points (posibly related to heat - read: valves). In such cases I also do not advise to resolder everything - you have to find out exactly what needs to be fixed. ANd only then you can think whether you need to replace some caps.
In your case it would be quite easy to determine (at least) whether the problem is related to the preamp or to the power amp. Have you checked it? You can simply test it by plugging in the bass into the power amp in (when the problems appear again). I could fix it but I'm also not located in UK. Try with StevesAmps.

Mark

[Nostromo]

Thanks for that Mark . . . . I'm sure your advice is good . . . and your way ahead is exactly the one I'm going to adopt.

The info I got from Psycho Bass Guy, (the knowledgeable contributor to the "Vintage Amps Bulletin Board") suggested that all Custom Shop Rumble Bass 300w heads had serious problems. And after lots if internet research I read from various sources that a good percentage of these amps broke down very quickly from new, many in retail stores, after only hours of being demo'd, and before they could even be sold ! ! These infant breakdowns, and there were lots of them percentage wise apparently, went back to Fender and most never saw the light of day again as even fenders warranty repair people couldn't fix them ! . . (that quote was from the guy responsible for the custom shop warranty returns at the time) So, a strange backlog of stories and history behind these rare amps ? . . I’ve never even seen another example in the UK in the flesh other than my own, so I don’t know if the problems reported on the internet applied to the UK batch the same as it certainly did to the USA 110v ones ? . . . . I’ve also read there were less than 30 sold in the UK all together.

I noticed that the Bass Player with Neil Young (Rick Rosas I’m pretty sure it was ?) was using a Custom Shop Rumble Bass head at Neil Young’s Glastonbury gig in 2009 I spotted it on the TV and that’s the only time I've ever seen one being used. (That would make sense as the Rumble Bass was closely associated [design wise] with the AMPEG SVT which Rick Rosas generally used) It would be interesting to know whether that example (probably a 110v model) is still original or whether Rick Rosas has had to have his modded to make it tour reliable ? ?

Anyway, my intention is to let Steve Rowse have a look at mine and see if he can fix it without having to do too much to detract from its originality ? . . . so, thanks for your thoughts and here's a picture of my Rumble Bass which looks lovely but sounds terrible at the moment ! ! !

[attachment=74789:Rumble_Bass.jpg]

Cheers,

Edited March 14, 2011 by Nostromo

[molan]

Another big +1 for Steve R.

He cured a problem on my SVT II that two other repairers failed to find

[MarkBassChat]

Can you post a photo of the amp from the back? I assume that the fan is working. Have you checked whether the problem is with the preamp or the power amp?

Mark

[attachment=74790:FenderRumble2.jpg]

[Nostromo]

[quote name='MarkBassChat' post='1162108' date='Mar 14 2011, 06:14 PM']Can you post a photo of the amp from the back? I assume that the fan is working. Have you checked whether the problem is with the preamp or the power amp?

Mark

[attachment=74790:FenderRumble2.jpg][/quote]


Hi Mark,

Yea - I will post up a rear elevation shot of my amp as soon as I next connect my camera to my lap top . . . . but, for info, mine looks just exactly the same as the one in your post . . . . is that your amp ?

If so, have you ever had any problems with yours ? . . . . .

For info, I've just found a couple of old obscure posts (90's) saying that some of the Rumble Bass Amps had duff valve sockets and that otherwise unfathomable problems could sometimes be resolved simply by upgrading the valve sockets ?

And yes . . . my fan is working fine . . . . but its odd that the fan directs airflow over the transformer when its the main chassis units that allegedly get the hottest ?

Havent checked out whether pre or power side problems as I dont know how to do that ?

Cheers,

Edited March 14, 2011 by Nostromo

[MarkBassChat]

[quote name='Nostromo']Hi Mark,

. . . . is that your amp ? If so, have you ever had any problems with yours ? . . . . .[/quote]No, it's not mine but I heard of several guys who do not have any problems with this amp.
[quote name='Nostromo']For info, I've just found a couple of old obscure posts (90's) saying that some of the Rumble Bass Amps had duff valve sockets and that otherwise unfathomable problems could sometimes be resolved simply by upgrading the valve sockets ?[/quote]I wouldn't believe in everything what is on the internet. This is a high power amp and the valve sockets are the components that get a lot of heat. And they sometimes can even get desoldered. On your place I would check how the power valves sockets look like and whether they ar still soldered correctly. The airflow in this amp could be a little bit stronger (what about a more powerful fan?) but first you have to fix the amp. You could compare the airflow of the fan in this amp with a fan in similar amp - Ampeg SVT-CL (I have somewhere data for this fan). And yes, in SVT-CL the fan directs airflow directly over the power valves. This may be an important difference.
[quote name='Nostromo']Havent checked out whether pre or power side problems as I dont know how to do that ?[/quote]This is simple, next time when you have problems with the amp (so maybe right now) just plug a bass into POWER AMP INPUT socket on the rear of the amp. There will be still noise if the problems are caused by the power amp. But if the are caused by a preamp (this is less likely), there will be no noises.
You can also plug a Jack-Jack cable into EFFECTS SEND and RETURN - often dirty sockets cause strange nioses.

Mark

[Nostromo]

Many Thanks . . . . .

I will check out as suggested.

Cheers,

[Sunburst79]

Hello. First post.

I have a working 1996 Rumble Bass Stack (head and 2 410 HF cabs).

I had a bit of an issue with crackling and the volume going up and down. Checked the tubes which were original and fine. Reseated the multi pin amp to chassis connector a few times. The Amp worked for about a day and then the noises came back. I decided that the next logical step before taking it to the shop was to clean and lube the pots - although none of the pots were actually scratchy. Which I did. I also tapped and probed all of the caps and resisters with the unit while running and none of them were particularly microphonic or intermittent. These units seemed to be designed to be field serviced and for whatever reason Fender used 148 "Fast-On" Connectors! (Spade terminal connectors) to connect various sub assembly's to the main circuit board. While the unit was apart I made point of going through and rocking each connector to ensure it was making good contact. A bad connection here is going to act exactly like a cold solder joint. Its worth taking your amp apart and checking these connectors. My amp has been flawless since July of 2010 After doing this. Normal precautions about working on high power amps apply. It worked for me and hopefully helps someone. I've never played through a vintage Blue Line SVT but this thing has noticeably better tone then my mid nineties SVT CL 810HE.

Edited April 14, 2011 by Sunburst79

[kevin_lindsay]

I had the exact same rig around 2002 and I was fortunate never to have any problems with mine. I had mine in full flight cases, and sold it to the owner of the 'American Guitar Store' who I then bought an Alembic Mark King from.
I wonder where that rig ended up?

[Sunburst79]

Mine came out of Studio Rentals in LA, While its in fair shape cosmetically its got enough wear that I would say it must have been a pretty popular rental unit. I'm glad to have it.

[Nostromo]

[quote name='Sunburst79' post='1193484' date='Apr 9 2011, 03:54 AM']I have a working 1996 Rumble Bass Stack (head and 2 410 HF cabs).

I had a bit of an issue with crackling and the volume going up and down. Checked the tubes which were original and fine. Reseated the multi pin amp to chassis connector a few times. The Amp worked for about a day and then the noises came back. I decided that the next logical step before taking it to the shop was to clean and lube the pots - although none of the pots were actually scratchy. Which I did. I also tapped and probed all of the caps and resisters with the unit while running and none of them were particularly microphonic or intermittent. These units seemed to be designed to be field serviced and for whatever reason Fender used 148 "Fast-On" Connectors! (Spade terminal connectors) to connect various sub assembly's to the main circuit board. While the unit was apart I made point of going through and rocking each connector to ensure it was making good contact. A bad connection here is going to act exactly like a cold solder joint. Its worth taking your amp apart and checking these connectors. My amp has been flawless since July of 2010 After doing this. [color="red"][b]Normal precautions about working on high power amps apply.[/b][/color] It worked for me and hopefully helps someone. I've never played through a vintage Blue Line SVT but this thing has noticeably better tone then my mid nineties SVT CL 810HE.[/quote]

Thanks for the above advice Sunburst79

What are the normal precautions that apply when working on high power amps ? . . . . I know there are issues about high voltages inside valve amps . . . and as Im a mechanical engineer and not an electrical one this has always put me off tinkering ?

Are there easy steps that can be taken to discharge any potentially dangerous components so that you know the amp is safe to work on ?



Cheers

[Thornybank]

My tech sorted my Rumble.
Some obvious ''need' tweaks in the design.

Packing and courier cost figures, but he is tippie top and only charges for true work time.

[Thornybank]

[quote name='Sunburst79' post='1193484' date='Apr 9 2011, 03:54 AM']Hello. First post.

I have a working 1996 Rumble Bass Stack (head and 2 410 HF cabs).

I had a bit of an issue with crackling and the volume going up and down. Checked the tubes which were original and fine. Reseated the multi pin amp to chassis connector a few times. The Amp worked for about a day and then the noises came back. I decided that the next logical step before taking it to the shop was to clean and lube the pots - although none of the pots were actually scratchy. Which I did. I also tapped and probed all of the caps and resisters with the unit while running and none of them were particularly microphonic or intermittent. These units seemed to be designed to be field serviced and for whatever reason Fender used 148 "Fast-On" Connectors! (Spade terminal connectors) to connect various sub assembly's to the main circuit board. While the unit was apart I made point of going through and rocking each connector to ensure it was making good contact. A bad connection here is going to act exactly like a cold solder joint. Its worth taking your amp apart and checking these connectors. My amp has been flawless since July of 2010 After doing this. Normal precautions about working on high power amps apply. It worked for me and hopefully helps someone. I've never played through a vintage Blue Line SVT but this thing has noticeably better tone then my mid nineties SVT CL 810HE.[/quote]


Nice to see another.
I have the same tan/oxblood with one HF and one LF 410.

[escholl]

[quote name='Nostromo' post='1160421' date='Mar 13 2011, 02:07 PM']...motor-boating noises, crackling & popping noises, and intermittent volume loss...
Nostromo[/quote]
[quote name='Sunburst79' post='1193484' date='Apr 9 2011, 03:54 AM']These units seemed to be designed to be field serviced and for whatever reason Fender used 148 "Fast-On" Connectors! (Spade terminal connectors) to connect various sub assembly's to the main circuit board. While the unit was apart I made point of going through and rocking each connector to ensure it was making good contact. A bad connection here is going to act exactly like a cold solder joint. Its worth taking your amp apart and checking these connectors.[/quote]
Don't know if you have this fixed yet Nostromo, but Sunburst79's advice is exactly what I would suggest. It sounds to me exactly like either a dirty/poor valve socket or dry joint/loose spade connection.

[quote name='Nostromo' post='1260976' date='Jun 8 2011, 11:31 AM']Are there easy steps that can be taken to discharge any potentially dangerous components so that you know the amp is safe to work on ?[/quote]
Well, if you don't really know what you're looking for then the easiest way is probably to just take a voltmeter, and measure across any capacitors in there (obviously with the unit off). This will do two things, it will tell you if there is any potentially dangerous voltage present (generally considered to be >50V), and it will also drain out that voltage through the high impedance of the voltmeter...how long it takes will depend on the cap size and the meter impedance. May take a little while on big caps to get down from 400-ish volts to below 50, but most of the caps should be drained naturally after a minute or two anyway, just by shutting the amp off. Most amps drain within a few minutes of shutoff, some may hold a charge for a little while.

If it's not been used recently it is almost certainly perfectly fine, although always a good idea to be cautious anyway.

[Sunburst79]

Hello Gents.

Just thought I would stop by and not that the amp has been quiet and trouble free for over a year now.

I still suspect that the main culprit is all of the spade connectors.

[Nostromo]

Hi everyone and thanks to all who have contributed to this topic.

Well . . . . . . GOOD NEWS ! . . . . . . my Rumble Bass is fixed and working again.

My problem was different to any of the issues mentioned within this thread so here's what my Amp Tech told me in a recent email on the subject:-

"Very simple in the end, really - the bias sensing resistors were significantly out of spec, which meant that it was running way too hot when it seemed to be correctly biased. This is actually difficult to check because the resistors are only 1 ohm, which means that you can't meter them directly because a normal multimeter isn't accurate enough. (My test probe error alone is at least .3 to .4 ohms.) I found it by comparing the apparent reading from the sensing resistors to an accurate measurement using the output transformer - after realising that the power valves did seem unusually hot even for 6550s. Being out of spec was almost certainly just caused by heat over the years. So - I've replaced all the bias sensing resistors with wirewound resistors which are immune from this problem. (The originals were cheap carbon comp or carbon film, hard to tell which.)" . . . . "The amp is running fine now after a 6 hour soak test at full volume indicated no overheating or noise problems apparent".

So, if any of you guys lucky enough to own a Bruce Zinky Custom Shop Rumble Bass Head run into any overheating problems then do consider the bias sensing resistors as a possible cause of the problem. . . . It was obviously a very cheap fix for me !

Cheers all.

[Nostromo]

Still going strong eight years later !!!... and I found another one ... which needed the same mods !

Edited August 29, 2019 by Nostromo

[Nostromo]

And still working ok - 100% reliable and with no problems so far in 2022 😀

[Downunderwonder]

Who was that masked Tech? Put his name in lights!

[GrowlyBassDude]

Great that your amp is sorted and holding. The Zinky-era Fender CS amps are not great across the board in my experience. I had a Tonemaster head that also motorboated and stumped a couple of techs. Thats when I taught myself how the repair amps (back in the early 2000s). Those IC-branded filter caps are garbage. If your amp still has the original filter caps, it would be worth having someone do a cap job and using some good-quality caps like F&T brand. 

[Nostromo]

Well here we are in August 2023 and both amps are still running 100% trouble free. Still thinking about upgrading the filter caps but almost frightened to do it due to the old "if it aint broke don't fix it" adage !!!

 

Cheers.