Dumble Serial number 006X OD50WX

[pompeiisneaks]

This was posted in the for sale trade as on reverb today, seems one maybe we haven't seen before?

I grabbed the pictures and here they are.

Figure if it's one we haven't seen maybe people will reverse engineer etc.

~Phil

[pompeiisneaks]

I'm wondering if this is a clone, there's a wima cap in it? Or did someone fix a bad one with the wima?

It has the engraved boards like he used to do back at the start, or so I hear?

~Phil

[dbeasley]

That wima cap looks like it came later. Notice the solder joints on it and the others.

If that amps a fake, I'd say it's a pretty good one.

Sent from my moto g(6) using Tapatalk

[andyhardy]

It looks photoshopped or modded
the od entrance is missing the 1.2 meg and
V1b has no bypass cap

[Guy77]

I can see were the future is going with these rare amps . I believe it will be like the paintings made century's ago from famous painters. These painting now need to be stored in climate controlled conditions and maybe these amps as there value sky rockets will need to be stored in the same way!



Cheers

Guy

[Mr. dB]

That wima cap looks like it came later. Notice the solder joints on it and the others.

If that amps a fake, I'd say it's a pretty good one.

Sent from my moto g(6) using Tapatalk

The amp has a voltage selector, so if it has lived in Europe the WIMA MKS-4 cap would be a standard service replacement part there.

[Mr. dB]

V1B cathode is not bypassed?

[Mr. dB]

Here's the 06x amp side by side with the 03x amp that came up for sale last year:

[GPD]

An interesting amp,

This very clearly is a genuine article late 1970's ODS...no doubt about it. It also, very clearly, has been modified a little bit. Other than the obvious reality of the Fender Woodward/Schumacher PT being an export model, the model number itself "OD-50WX" tells you it was an export model..."X" meaning export. I'm not so positive that the serial number is 006X...I think it might be 008X...plenty of evidence that it was assembled in 1979.

Realistically, just looking at the chassis alone tells you all you need to know. Nobody on the planet has ever accurately reproduced one of these 1970's 50W/100W (Not even Jelle ). the right alloy, the right thickness main chassis, the right thickness and style gussets, the right PEM studs and nuts, the right surface finish, the right welds on the gussets, etc. The positioning of the silk screening alone is a dead giveaway...I've yet to see anyone get one of these chassis right.

Then looking into the guts...

The Black FR-2 Fiberglass boards are obviously original Dumble parts. Good luck finding this exact same material today. Then you've got the Dale RN65 plate resistors on V1 & V2 as well as part of the polarity splitter. These are very obviously 1970's vintage as evidenced by the bulbous end caps. If they are 100K's on the plates, which is likely, this is a value that is essentially impossible to source with 1970's date codes. You can see the Sangamo 510pf silver mica cap, the IRC MEB cathode resistors throughout. Anyone had any luck finding some NOS IRC MEB's in 1.5K lately? Those are real-deal, single-stripe foil indicators of 1970's Sprague 6PS orange drops. You can find them...but not so easy or cheap either. Then a plethora of 1970's vintage Piher carbon films including the 1 Watt feedback resistor correct for this period Dumble. And how about that brown molded EKC (Electra Corporation) 1 Meg resistor? Good luck finding one of these. Or how about the CalRad DPDT "Ice Cube" Relay? Think you could find one?

Then there are the pale orange Sprague Atom Electrolytics all date coding to prior to 1979. And the ICC lytics (International Capacitor Corp.)...these are actually Japanese made parts...Dumble used them along with Sprague TVA's depending on the amp. Then you've got the MF6 and the RN65 (MF7 size) Electra- Midland resistors soldered into the polarity splitter circuit. These are likely late 1960's or 1970's vintage parts...not to be confused with the later MEPCO/Electra versions that are more easily found today but still very scarce.

And the 1960's/1970's era Cinch tube sockets...typical of a Dumble. Then you've got the old production thumb wheel adjust Piher on the FET board...the markings are a dead giveaway of the vintage of the part. Piher still makes and sells these but they are not constructed the same. The FET itself? Good luck finding one with those markings on it. Another clue is the pilot lamp...this can be found on many 1970's Dumble products. It was a plastic housing part available in multiple colors...he seemed to use different color lenses on different amps for whatever reason. This is a long defunct GC Electronics panel lamp part number...I haven't see one appear anywhere for decades. The knobs are the correct flat insert (not concave) and the mini toggles...1970's vintage Miyama's...long gone. Miyama is still in business but the P/N's Dumble used have been obsolete for decades as are the cool correct red bat covers that go with them.

Then study the solder connections...those that haven't been molested and they are clearly Dumble's work. Dumble would occasionally use Radio Shack "Archer" tan carbon film resistors...you can see a couple of these on the FET board. These definitely are not the tan Draloric made Sprague Q-Line's that he would start using in the early 1980's. The LV supply tranny I cannot see the markings but Dumble generally woulds use a CalRad or Archer part here...though sometimes a Triad...just depended on the specific amp...no rhyme or reason...but what is in there looks right.

Only one cabinet shot...the suede looks extremely nice for the age of the amp...but without seeing more angles...hard to tell if the suede is still original. The speaker is likely an Altec 417 judging from the aluminum dust cap...very much expected for this amp. The aluminum trim on the face of the amp is 100% correct...most that copy a Dumble never get the thickness of this material correct. Even the power cord is correct for that vintage Dumble amp.

The coax looks very RG59-ish...I would have anticipated Columbia Flex-Foam but obviously not in this case here. He used a variety of different RG59's...most are familiar with the Tandy branded cable but I've seen Columbia RG59 in some amps. The markings and P/N are hard to read unless you see the cable up close.

Anyway, you get my point...no way this amp is not an original Dumble.

I see some comments on the mysteriously missing 1.2MEG resistor. Usually, everyone expects to see a 220K in series with a 33K in parallel with the 1.2MEG...do the math, this is 209K. Now look at this amp...you've got a 100K and 110K in series or 210K. The stray carbon comp in this position is a bit surprising but nobody said this is how Dumble originally built it? Right? This could easily have been changed and looking at the solder joints...I say it was.

The missing cathode bypass cap? Well look closely at the bend angles on the leads of the IRC 1.5K cathode resistor...you can see that it originally had the bypass cap right next to it. If Dumble intended to not have this cap, he would have run the leads at a straight shot...this has been changed. Why? good question...maybe to reduce bass? I'm not sure...hard to tell.

Same goes with the WIMA...I highly doubt the .1uf 6PS failed, this appears to be some tone sculpting experimentation.

The extra small value ceramic disc caps in the V2 portion of the circuit that you don't expect to be there...could be original...might not be...again, looks to be a bit of tone tweaking or perhaps there was an oscillation to be dealt with. Hard to tell without the amp on the bench.

Anyway, anyone who's actually played one of these original 2nd/3rd generation ODS's can appreciate the raw nature of their OD content. You can never really balance the clean/dirty tones like you can with the later ODS's but there is a nasty quality to the OD that is ever so appealing to my ears. I like the cleans too...fun amps...definitely something more evolved than the Boogie's he was competing against at that time.

Always fun to see another one of these amps surface...especially with the gut shots.

GPD

[Max]

I'm not so positive that the serial number is 006X...I think it might be 008X...plenty of evidence that it was assembled in 1979.

Correct:

"... 3rd generation made around 1978-1979 Ser# around 60-75. ..." Source: https://ampgarage.com/forum/viewtopic.php?f=5&t=12871

... Fiberglass boards ...

Correct:

"... synthetic resin bonded paper, a composite material made of paper impregnated with a plasticized phenol formaldehyde resin, ..." Source: https://en.wikipedia.org/wiki/FR-2

... I would have anticipated Columbia Flex-Foam ...

Correct:

... "In the 3rd generation "pre-classic" amps you find a different coax cable. It is not the "Columbia Flexfoam 1389" of the 2nd generation ODS amps but a usual black RG59 foam 75ohm video cable. It looks very similar as the black Tandy Wire RG59 of the transition generation and 4th generation amps but it is not marked "Tandy Wire". These different coax cables may well be one of the reasons for the different tone of the 3rd generation amps in addition to the small tone stack differences between 2nd and 3rd generation amps. ..." Source: https://ampgarage.com/forum/viewtopic.p ... 99#p163699

To avoid misunderstandings: AFAIR you'll find the black RG59 without the "Tandy Wire" label in some of the 2nd generation ODS amps in the range between #0040 and #0060, too.

Two personal observations in regard to OD-50WX #006X (of course without intending any kind of personal interpretation): 4 holes for preamp tube sockets; no preamp-out coax; unusual looking Bassman(?) OT.

Cheers,

Max

[erwin_ve]

I see some comments on the mysteriously missing 1.2MEG resistor. Usually, everyone expects to see a 220K in series with a 33K in parallel with the 1.2MEG...do the math, this is 209K. Now look at this amp...you've got a 100K and 110K in series or 210K.

GPD,

Interesting! You seem to know a lot on the specific parts that are used? Thanks for posting that!

On the od entrance: the 220k is not in series with the 33K. They both go to a ground point. If they are in series, as you said, the grid is missing a ground reference. So something else is happening, fe both resistors have a bypass cap. Never seen it before.

[didit]

On the od entrance: the 220k is not in series with the 33K. They both go to a ground point. If they are in series, as you said, the grid is missing a ground reference. So something else is happening, fe both resistors have a bypass cap. Never seen it before.

I arrived at similar puzzle after first glance last week. Someone'll figure it out. Unfortunately insufficient pixels at necessary angles to see everything.

Best .. Ian

[hitchcaster]

I'm not so positive that the serial number is 006X...I think it might be 008X...plenty of evidence that it was assembled in 1979.

Correct:

"... 3rd generation made around 1978-1979 Ser# around 60-75. ..." Source: https://ampgarage.com/forum/viewtopic.php?f=5&t=12871

... Fiberglass boards ...

Correct:

"... synthetic resin bonded paper, a composite material made of paper impregnated with a plasticized phenol formaldehyde resin, ..." Source: https://en.wikipedia.org/wiki/FR-2

... I would have anticipated Columbia Flex-Foam ...

Correct:

... "In the 3rd generation "pre-classic" amps you find a different coax cable. It is not the "Columbia Flexfoam 1389" of the 2nd generation ODS amps but a usual black RG59 foam 75ohm video cable. It looks very similar as the black Tandy Wire RG59 of the transition generation and 4th generation amps but it is not marked "Tandy Wire". These different coax cables may well be one of the reasons for the different tone of the 3rd generation amps in addition to the small tone stack differences between 2nd and 3rd generation amps. ..." Source: https://ampgarage.com/forum/viewtopic.p ... 99#p163699

To avoid misunderstandings: AFAIR you'll find the black RG59 without the "Tandy Wire" label in some of the 2nd generation ODS amps in the range between #0040 and #0060, too.

Two personal observations in regard to OD-50WX #006X (of course without intending any kind of personal interpretation): 4 holes for preamp tube sockets; no preamp-out coax; unusual looking Bassman(?) OT.

Cheers,

Max

nah thats not bassman size... thats vibrolux, bandmaster, etc smaller trannie style... usually on ultraphonix amps of that size, like a bandmaster he would pull the OT and put in a much bigger bassman... same size as super reverb.. so interesting to see the smaller trannie on this build. i just demo'd a stock vibroux and tried a vintage bassman in it to see what happened.. it was "bigger" sounding, but the smaller stock OT sounded and felt better to me so i put it back in.. maybe a UP modded amp id feel different.

[GPD]

OK,

To add to the discussion...I noticed the seller specifically called out 006X serial number...so I took a closer look at the supplied image and with a little help from Photoshop tools I can definitely see the "6" now. HAD used your typical "Numberall" hand stamp. The numeral font matches up exactly to a character set I actually have in my own Numberall stamp. Anyway, check this out...a little collage between some real 1970's vintage Dumble amps with a S/N in the 80's, another Dumble with the S/N in the 60's and the amp in question. You can clearly see the "6"...so that jives with the range of serial numbers we'd normally expect from this generation of ODS.


Back to the more obvious circuit changes. Yes, I'm well aware that the two resistors in the divider network in the 2nd & 3rd generation ODS's (220K & 33K) are tied to ground. The purpose of the 1.2MEG and the 33K is to provide a 36:1 attenuation of the signal from V1A/B into V2 (OD). If there is not a ground, you don't have ad divider network. By removing the 1.2MEG, replacing the 220K & 33K with 110K & 100K resistors it seems very obvious that the ground (underneath the board) has been lifted. Now what you have is an "Equalization Network" and the attenuation is gone. I'd be willing to bet there is 50-60V Peak-To-Peak hitting the grid of V2 once the relay is activated. Somebody must have been wanting some outrageous gain which, would of course, be of the square wave variety in this proposed scenario. Also, the hum and hiss levels will be greatly increased given Dumble never regulated the filaments. We'll never know for certain what is under the board unless it were to be pulled (unlikely).

OK, now what about the missing cathode bypass capacitor? Well, with all the gain coming off of V1, removing this will definitely reduce the gain to V2...probably not nearly enough but it will help somewhat. Then there is the physically small ceramic cap across the 100K Piher. This is an edge enhancement tweak (pre-emphasis). I'm not sure of the value but it is likely 100pf or less. Then you've got the unexpected ceramic cap across V2A's Dale plate resistor...this obviously is in place to attenuate high frequencies.

So, at some point after Dumble shipped it to Europe the amp was modded to alter the nature and type of OD it would produce. Of course, it would be very simple to put this back to stock, not much really to change. All the impossible to source parts are still in the amp. A couple of Pihers, a 6PS...now finding the tan metal film 1.2 MEG...that's not so easy.


GPD

[Max]

... some real 1970's vintage Dumble amps with a S/N in the 80's ...

Just to avoid misunderstandings: Up to now I've never seen a 1st, 2nd, or 3rd generation ODS chassis with "a S/N in the 80's". So, if you should know of a 1st, 2nd, or 3rd generation ODS chassis with "a S/N in the 80's" pictures of the complete front and back would be very interesting.

... So, at some point after Dumble shipped it to Europe the amp was modded ...

Some examples for some mods implemented by the european importers at the order of their customers:
4th preamp tube for a reverb circuit; 4th preamp tube for a buffered loop; additional passive or buffered loop input on the back instead of the "preamp-out"; modifications of the tone stack; etc.. And sometimes - for whatever reasons - the original Bassman OT was substituted by a Vibrolux/Bandmaster OT mounted by the european importers. And some of the european owners later ordered some european techs to mod their amps according to their individual personal taste.

Cheers,

Max