Gibsonette: Field Coil speaker question

[Leo_Gnardo]

Jonny, check your PM. My recommendation for a recone expert is there.

[Tom Phillips]

Jonny, check your PM. My recommendation for a recone expert is there.

Someone that all of us shouldn't know about?

[Leo_Gnardo]

Someone that all of us shouldn't know about?

Hi Tom,

I figured you californians had Orange County down south and A Brown Soun up north. Both good outfits, as far as I know.

I'll ask him if he wants his info in general distribution, for now check your PM.

[Tom Phillips]

My thinking is that we are building up an archive of knowledge. If some of the answers are provided off line then someone who reads this at a later date does not see all the information.

[Jonny toetags]

I'd use at least a 10w, probably more like a 20 watt. But it would help to know how much current would be flowing.

Voltage measured between the 2 pins is - 65VDC

[Leo_Gnardo]

My thinking is that we are building up an archive of knowledge. If some of the answers are provided off line then someone who reads this at a later date does not see all the information.

About Secret Recone Man: He's a one man shop, and may not want to be overwhelmed with trade. Let's let it be his decision. If he gives the go-ahead I'll put it up for the world to see. Who knows he might even join up with MEF.

[murrayatuptown]

Perhaps a little late, but here's my Gibson BR-9 project thus far. I think there is some useful info, if you can stay awake...oddly, I got no answers or interest on the Gibson web forum...oh well...

I had a Gibson BR-9 field coil speaker (8" I think) reconed at Circuitshop.com south of the airport in Grand Rapids, MI. I'm not sure they have all their recone details on the website.

I drove it there and picked it up since I am in GR regularly.

Took a week, if even that long, $45 + some tax, this past summer. I'd been meaning to do it since 1989...I guess it would have been cheaper then!

Preparing to work on the amp, I discovered the amp did not look at all like the Groove Tubes BR-9 schematic. More reading and I found there were 'transitional' BR-9 amps that had the circuitry of the GA-9...mine has parallel single-ended 6V6's with a single preamp tube and no interstage transformer.

My field coil: high-resistance winding 750 ohms, low resistance winding very low, I think less than an ohm, don't have that info at my recall. Shop felt 750 was in range of normal, and I gather from reading elsewhere that the low resistance winding is probably a hum-bucking winding that is wired in series with the voice coil, with polarity selected by experiment (lowest hum).

Mine had been modified in 1988 due to the open voice coil - a local shop installed a PM speaker for me, and a supplemental choke instead of the common 1000 ohm resistor.

I was bothered by the vague marking on the output transformer and had not been able to find any pictures of the correct one online anywhere. The power transformer was marked BR-9 with a date (1952, week I forget) and mfr. number Magnetic Components Inc., parent company of 'Classic Tone' product line.

I e-mailed, and got some very interesting info back. Yes, they made the power transformer, but had only provided a sample in the 50's in response to a request from Gibson. They still had a file on the transformer, but were not selected as a vendor. I was told the voice coils on those speakers were quite commonly 3.2 ohms and many of the transformers were made by a company I was surprised I had not heard of. IIRC, the name was Rola (maybe in Ohio?, anyway, somewhere other than Illinois), and more digging suggests both Jensen and Rola were purchased by a Chicago company, IIRC, Swift, who were part of the meat processing industry in Illinois. I see Swift Transportation trucks on the highway and think I made a connection between them and the meat processor, but I might have hallucinated that part due to lack of sleep.

The transformer basic specs for the parallel single-ended version were 2500:3.2 ohms (27.5:1 turns ratio), and 70 mADC, and that it would have been marked GA9-O (GA-9 output). In closing , I was told they did not make a suitable transformer I could see as a replacement.

Meanwhile, I took the suspect transformer that had only 4 numbers on it (p/n or date code I have no idea, but two digits were 52, frustratingly possibly the same era as the power transformer, but the original should have been marked properly by whomever made it.

I took primary & secondary inductance measurements at 10 vac and also applied 1 vac from a variac on the secondary and measured the primary voltage.

I didn't repeat them here because they are only valid for 'ballpark' estimates. Transformer inductance has to be measured at the actual operating point as it varies drastically at other flux levels.

I got calculated and measured turns ratios between 11 and 13:1. Leakage inductance measurement showed there was no partially shorted winding (at the low voltage anyway, but it told me the transformer was not bad in terms of turns ratio and thus impedance ratio). So the transformer was actually wrong. Back to 1988...I didn't notice , didn't know how to handle the project myself at the time, and trusted an elderly radio repair guy...can't blame him, it may have been that way when I got it.

So, Circuit Shop asked me if I knew what the voice coil resistance was supposed to be...if it was 4 ohms... ("no idea, it's open" I said), said they'd look it up or figure it out physically from the wire remaining. A different person was there when I picked up the repaired driver, & he didn't know what was determined...

So I thought about this & wrote back to MCI - if I needed 2500:3.2 (or 4), was there any reason why I couldn't use a 5000:8 transformer for the same impedance ratio as 2500:4?

I looked at the Classic Tone 40-18031 which has a 7k primary with 5k tap and 8 ohm secondary, and 70 mADC rating.

The engineer acknowledged that yes it would work, but they hesitate to recommend higher impedance transformer designs for lower impedance applications as the current is higher, in general. It would run a little warmer, but would be OK.

I suspect it may have more primary inductance for the 5k and 7k application and thus may have more low end at 2500. Considering I turned the thing on twice since 1988, I don't think I'm going to overheat it.

So I got one for Christmas, and MCI would like to see a pic of it installed.

This was the only identifying info I was able to obtain with online research, so I think it's the closest thing I'll find. I was given the amp by a guy who repaired a Gibson guitar for me in 1988, with the qualifier that I keep it as original as possible.

I didn't do the transformer mixup, and rewinding isn't an option since I had mystery iron anyway.

So, $90 invested over 26 years isn't bad (I didn't count the cost of replacement electrolytics yet - I bought a bag of 100 to make them seem economical) (?!?that makes sense, now doesn't it?!?)

Not done with it yet...just resuming the project...again...

murray

[audiopete]

Try Weber again - try calling. I had a Leslie 15" reconed by them and it was excellent. I would get this amp back as original as possible. Gibsons aren't worth what Fenders are, but a 50s Gibson would be the most valuable of the Gibsons, I would imagine. I can also see these amps going up in value as less people can afford vintage Fenders and Marshalls.

[audiopete]

I bought a bag of 100 to make them seem economical) (?!?that makes sense, now doesn't it?!?)

Now this I don't get. For a project like this I would think being economical would be the least of the priorities. For $30 or $40 in good caps usually, why wouldn't you get the best? When you have to go and replace a cheap cap that blew a month after you installed it, you will wish you just put quality parts in the first time.

I've repaired my share of blown cheap caps and I get paid to do it, but this is the last place I would ever go cheap when it's my choice. I could see if you are manufacturing 1000s of units and want to save money, but then you should expect warranty claims.

[gcmillgc]

Enzo I have an early Gibsonette guitar amp (two inputs, no tone control, says it is 75 watts - no model number available. So it works, I am going to replace the tubes and there are a couple of electrolytics in it that probably need replacement. One of them (on the power supply) is a 10 -10 microfarad @470 volts. Been looking at tube depot etc, and they don't seem to have any 10 - 10 microfards. They have 20 - 20 but that wouldn't work. Any idea where I can get one of these, and as an alternative could I put in two regular 10 Microfarad caps, or is there something special the one 10 - 10 cap does that two discretes could not do (or blow it up??) I would like it original same parts, but this animal is hard to find. Any ideas where I could get one? Got the four tubes covered with JJ's. Thanks... G

[gcmillgc]

Forget cheap electrolytics you get what you pay for. Go with a good brand, I like Spragues - they are accurate and last a long time. Pay a few bucks for one - it will work perfectly.

[Enzo]

I don't know why a 20-20 would not work. Ought to work fine. Back then they used dual caps like that to save space. I would just use two individual caps and wire them as appropriate.

here is a 10-10/450
https://www.tubesandmore.com/products/C-ET10-10

[gcmillgc]

Thanks, Enzo. I will replace with two discretes. Really appreciate you getting back with knowledgeable advice, also on my Behringer question. G

[murrayatuptown]

Sorry, that's my weird sense of humor...of course I spent more on a bag, but I have a lot and can do other things with them :O)

They were Panasonic/Matsushita. Once I got them, I looked up their spec sheet, but forgot what I found...have to look it up again.

On eBay, you roll the dice...

When I have to order capacitors for repairing a piece of machinery (for example, rebuilding a power supply in a motor controller), I make sure my options (like Digi-Key or Mouser to eliminate the dice roll of whether what I order will be what it's marked as) will physically fit where needed, then pore over the electrical variables. I look for the highest temperature/life rating and the highest ripple current ratings. I do not know how to figure out when/where I care about ripple current, but higher is better for life-span...so I pick the option with the highest ratings for those parameters, and ignore any voodoo opinions about which ones sound better...same logic you advise... fix it once...cheaper than redoing it. The highest ratings weren't always the most expensive..maybe certain ones (capacitance, voltage, etc.) are used so frequently they cost less to make.

Trivia for the younger crowd (silver-backs may already know):

Former Sprague manufacturing plants that changed names (at least one of the two following may be employee-owned now):

SBE (Orange Drop manufacturer) is named for Sprague Barre (Electronics), in Barre, Vermont.
BMI is Barker Microfarads, Inc., a former Sprague electrolytic facility in Virginia [url=http://www.bmicaps.com/about-us/] Not sure how many consumer products use them...do a lot of mil-aero due to the established reputation (performance, existing qualifications, compliance with rules, etc.

[murrayatuptown]

I get tired of reading posts about "fake parts". It's become such a commonplace topic it seems no one trusts anything...but they don't use the word 'counterfeit'...

In my search today to identify the electrolytics I bought on eBay a few years ago, with enough knowledge to figure out what I was looking up, I could not find a current or discontinued Panasonic part number that has both the marked ratings, lead spacing and physical size. Initially I thought 'well, I haven't found it yet'.

Once I found a Panasonic data sheet for the series I have, I could 'create' a part number to go with what I have, then search high and low for it. Nothing. Broader search within Digi-Key and Mouser revealed only two parts in this package size and lead spacing, made by two other companies.

I got Panasonic [M] EB series 22 uF 450V +105C parts with 5 mm lead spacing and 12.5 mm diameter, 25 mm height. I would expect a p/n something like EEUEB2W220___ (blanks are add'l parameters I can't be sure of). I can only locate 16 mm and 18 mm diameter EB capacitors with 7.5 mm lead spacing on Panasonic/Matsushita site. Current datasheet from Digikey is 2013 with qualifier that specifications are subject to change. They don't typically make later series larger...they tend to reduce size if not keep it the same...or add new sizes...not delete one size offering.

I am pretty sure I have a good reason to buy fewer things on eBay if I care what I actually receive.



Lastly, photos of Panasonic parts in this series have a built in 'riser' shape in the rubber 'seal' of the electrolytic capacitor 'can' (mine are flat & smooth), and the stress-relief pattern at the closed top of the 'can' is dissimilar arcs on Panasonic photos, but an ordinary X or cross-hair pattern.

No date code was a surprise, too, but maybe they put it on packaging nowadays...they used to have their own (Japanese) letter/number coding instead of our typical WWYY numeric datecode.

Like GGMILLGC said, you get what you pay for (hopefully).

Since I don't know what brand they really are (came from China...Chinese?), why should I trust the voltage rating? If they aren't Panasonic, then I don't get to enjoy the warm fuzzy feeling I had some idea I knew their ripple current and lifespan ratings because the datasheet is no longer relevant. Maybe I put two in series and cross my fingers.

Grrr