Restoration of Kalamazoo Tube Guitar Amplifier

[davidguilbault]

Hi folks,

I am restoring/modifying a Gibson Kalamazoo Reverb 12 guitar amplifier and need some guidance.

This is a 12-watt, hand-wired, point-to-point amp, with 10" 8-ohm speaker, tremolo oscillator and spring reverb tank. The preamp stages are run by 12AX7 tubes, as is the phase inverter and the reverb driver - 3 12AX7 tubes in all. Power output tubes are 2 6BQ5/EL84 tubes. The previous owner updated the amp with a 3-prong power cord. V1 is preamp stage one & tremolo oscillator, V2 is preamp stage two & phase inverter, V3 is reverb driver, and V4/V5 are power outputs.

An amp tech here in Seattle looked at the photos of the chassis innards and said that the orange capacitors are bulletproof and don't need changing. But, he did say I should change out the black caps and the big "dual section" capacitors.

Another TK'er has offered to replace the caps if I order new ones. Problem is, this is all Greek to me. Can anyone identify the caps in my amp from the schematic and photos below? And from where would I order their replacements?

UPDATE: This thread will serve as a running log of the progress of the restoration/modification.

Thanks for your time and consideration.

Hope all is well with you and yours.
Cheers for now.
David.

 

[tube-a-lou]

Bottom of the Schematic there's the listing 40/450volts, 20/450volts and 20/450volt,
there's the large cap with two red positive wires coming out of one end so it could be 20/20 or 20/40 you
have to turn it over to see what it is and on the other side middle of the schematic
there's a smaller cap, I see on the Schematic to the right of where it say's Amp
Connector there's a 10uf 25volt then there's one between the two 6BQ5 tubes there's
a small one and it says 25/15volts it's on the upper right. I have a smaller version
of this amp and there pretty nice.

Tube

 

[gogofast]

here are the electrolytics in red circles. all should be replaced before powering on. those orange caps are probably still good like your tech said, but i've seen some that had gone out of tolerance, so you might have to switch out a few of those as well.

you should install power cord strain relief as well. i have restored one of those and two model 1's and all of their power cords were just dangling with just a knot. great little reliable amps...though sound is nothing special.

 

[Sir.Byrd]

David, I'll see you later this week and we can discuss cap replacement.

 

[davidguilbault]

Here are the electrolytics in red circles. all should be replaced before powering on. those orange caps are probably still good like your tech said, but i've seen some that had gone out of tolerance, so you might have to switch out a few of those as well.

you should install power cord strain relief as well. i have restored one of those and two model 1's and all of their power cords were just dangling with just a knot. great little reliable amps...though sound is nothing special.

Hi gogofast. Thanks for the information.

The previous owner had a heavy-duty 3-prong power cord installed.

And young sir.byrd is going to help me replace the necessary caps. (Well, I'm gonna help him, as I am clueless and a danger with tools.)

Any advice on how to make the tremolo and reverb stronger? What do I fix in the circuitry for that? They seem a bit weak.

Cheers for now. David.

 

[davidguilbault]

Amp. Connector?

Another question: On the schematic there is a little rectangle labeled "Amp. Connector" which seems to be the white plastic 3-hole connector on the bottom of the chassis. What is that, and what is it for?

UPDATE: Found some photos of a modification that shows the plug that fits into that "Amp Connector". Looks like it connects to the reverb tank somehow. Why are there two connections on the schematic and only one on the chassis?

 

[tube-a-lou]

Is that for the Reverb to switch it on and off Only a quess? When I got my amp the
seller said the same the Tremolo wasn't working right, when I checked over it
someone put a lube in all the tube sockets, once I cleaned it all out it sounded
better. make sure you clean this guy out sockets, pots and everything.

Tube

P.S. How do you get those red circle on there?

 

[loomis]

When looking at your schematic, remember that -| |- is capacitor, usually measured in uf or mfd, and the zig-zag lines are resistors, measured in ohms. That should help you understand a lot of the schematic.

 

[davidguilbault]

When looking at your schematic, remember that -| |- is capacitor, usually measured in uf or mfd, and the zig-zag lines are resistors, measured in ohms. That should help you understand a lot of the schematic.

Excellent. Thanks Loomis. That helps me a lot. Cheers for now. David.

 

[davidguilbault]

First Restoration Steps

Hard to believe. But, I actually used a power sander for the first time today. (Now I am a man.)

Took the first steps in the amp restoration by stripping and sanding the cabinet and spray painting the corner and handle hardware "hammered grey".

Here's the cabinet before sanding.

UPDATE: Inside of cabinet spray painted black.

And here is the hardware after spray painting.

And so it begins ...

 

[Sir.Byrd]

Nice amount of photos in this thread.

 

[davidguilbault]

A Visual Story

Nice amount of photos in this thread.

I was a television, cable & Internet news producer for over 30 years - ABC News, CNN, PBS, NPR, MSNBC.com. I hope I can tell a visual story.

 

[Sir.Byrd]

Get the amp working first, then worry about that.

 

[davidguilbault]

Hammond/Gibbs Model C

Well, a little Internet digging around finds a 3-year old thread that quotes Accuronics as saying this amp had a Hammond/Gibbs Model C reverb tank. That is an Accuronics model 4FB2A1B. Specs for that tank are:

4 - Reverb type - Type 4
F- Input impedance - 1475 ohms
B - Output impedance - 2250 ohm
2 - Decay time - Medium (1.75 to 3.0 sec)
A - Connectors - Input grounded / Output grounded
1 - Locking device - No lock
B - Mounting plane - Horizontal open side up

Isn't the Web a miraculous place? And, ain't this journey of discovery fun?

 

[davidguilbault]

Edjumication

Get the amp working first, then worry about that.

No worries, Will. Just trying to "edjumicate" myself, chronicle this restoration journey and get some sage guidance along the way.

 

[davidguilbault]

Speaker Recommendations

I've asked speaker manufacturers which of their 10" models they would recommend for this amp.

This is my email to them:

"Hello. I'm having a Gibson Kalamazoo Reverb 12 guitar amplifier brought back to life. It's a hand-wired, point-to-point, 12-watt amp with three 12AX7 tubes driving the preamp, phase inverter, reverb driver and tremolo oscillator. And there are two 6BQ5/EL84 power tubes. I want to replace the vintage 10" 8-ohm speaker. I want the amp to be louder and don't want the speaker to break up. I'm looking for a warm, clean, articulate, jazzy sound. Which of your speakers would you recommend? This amp, by the way, is sometimes called the poor man's Princeton Reverb, if that helps any. Thanks for your time and consideration. Cheers for now. David"

These are their answers:

Weber - Model 10F150 with light dope for a warm, clean, articulate sound that stays clean.

Eminence - The Ragin Cajun for a very well-balanced American tone with chunky lows, crisp mids, and bell-like highs - a very efficient, clean and responsive speaker with a nice overall warmth.

Celestion - We’d recommend a G10N-40. You’d get some break up at higher output levels. But it’s a nice warm, even sounding speaker that would work well for jazz-type sounds.

The speaker currently in the amp is below. I'll likely keep that for awhile if the amp sounds fine after a re-cap.

UPDATE: Using a little online detective work and a strong magnifying light, I have determined this speaker to be the original 10" CTS speaker 10C1077 (Part # S-20003). Woo hoo.

UPDATE: Bought a Weber Ferromax Vintage Series 10" 10F150, 8-ohm, 25-watt ceramic speaker off ePay for a fairly good price.

 

[davidguilbault]

Tube Inventory

Here's my inventory of tubes to choose from for this project:

V1 - 12AX7 - Preamp stage One & Tremolo Oscillator
V2 - 12AX7 - Preamp stage Two & Phase Inverter
V3 - 12AX7 - Reverb Driver
V4 - EL84 - Power Output
V5 - EL84 - Power Output

For the EL84 slots I have a choice between Soviet Reflectors or Mesa tubes.

For the 12AX7 slots I have a choice between Sovtek 12AX7WB, Sovtek 12AX7LPS and vintage tubes (one each from GE, RCA, Sylvania & Silvertone).

UPDATE: Gonna put these retainers on, as the tubes hang upside down from the chassis.

 

[davidguilbault]

Tolex & Grill Cloth

Gonna go silver and blue.

 

[davidguilbault]

Kalamazoo Catalog

 

[davidguilbault]

Accutronics Guidance

Lovely response from Accutronics in Korea in response to my email question about which of their reverb tanks is right for my amp:

"Dear David. How are you David? Thank you very much for your email, but we are very sorry we cannot supply to you this proper reverb unit because we don't know every amp manufacturer spec. if possible, please ask to the service center of your amp manufacturer first and inform us their opinion. Then we can prepare your proper item soon. Please understand it well and inform us your opinion. However, I think the 4FB2A1C is good for your amp. Have a great day. Best regards / Park"

And here is part of a nicely detailed response from a US representative of the company:

Hi David:

How are you? Unfortunately, I have no idea which pan you need. You might check with service at Gibson headquarters or the internet forums to ask others. Check with distribution through CE Distribution or New Sensor. They supply service parts for most old amplifiers.

Please be careful about using components offered by Mojo Musical Supply (Mojotone) or Ruby (Magic Parts), because they will try to sell you a Chinese made copy, which may be acceptable for the application.

We are the manufacturer of reverb pans and only sell OEM to other manufactures directly. Customers are required to have in stock for up to five years after a product is obsolete.

We cannot make recommendations to a customer’s design, since they have various reasons for what they do and how they use our product. Be careful using another brand because Accutronics is completely different animal and cannot be replaced by any other brand.

However, many customers find the Belton pan a viable replacement. The Chinese copies burn so many out there all to save a few nickels.

The most important parameters are your input/output impedances.

Attached is a cross reference:
Accutronics pt#*************************************** Belton pt#
1EB2C1B**************************************** *******BS2EB2C1B
4EB2C1B*********************************************** BL2EB2C1B
8EB2C1B*********************************************** BS3EB2C1B
9EB2C1B*********************************************** BL3EB2C1B

Conversion Accutonics/Belton Type: 1 = BS2, 4 = BL2,** 8 = BS3,*9 = BL3

PART NUMBERING SYSTEM
Reverb part numbers consist of a seven digit code.
EXAMPLE: Accutonics Type 4EB2C1B = Belton Type BL2 (Belton long 2 spring) EB2C1B

Each digit in the part number represents a specification. The parameters are as follows:

1ST DIGIT = REVERB TYPE
2ND DIGIT = INPUT IMPEDANCE
3RD DIGIT = OUTPUT IMPEDANCE
4TH DIGIT = DECAY
5TH DIGIT = CONNECTORS
6TH DIGIT = LOCKING DEVICES
7TH DIGIT = MOUNTING PLANE
…

Another rule of thumb for cross references:
Old Fenders - AB
Old Ampegs - FB
New SLM Ampeg/Crate - BB
New Fender/Peavey/generic solid state stuff - BB

Thanks for the inquiry. Please let me know how it turns out for you. Hope this helpful and Good Luck!! Steve.