Help Schematic #97 Waikiki Tube Amp

mdyhrkopp

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Picked up a matching Lap steel & Amp set, Tweed Model #97 Waikiki, Labeled "Chicago Musical Instruments Co" 50 watt , has loctal tubes, 7Z4, 2 x 7C5,7F7,7C7 .
I have it working; I replaced 3 of the paper capacitors and now sounds good but think may still need some attention ? the 7F7 get warm not hot like the ones on the left and the 7C7 does not warm up at all :confused: doesn't seem right to me based on my little experience with tube amps. I can not find a schematic anywhere so far. There is one paper cap ( the horizontal one in picture) that I haven't replaced, my tube guy up town wasn't familiar with it, someone mentioned it may be a Power tube cathode by pass cap ? I also read something about the 7C7 being a pre amp tube and it draws very little voltage ? I'm learning as I go, any help on this amp would be greatly appreciated !
 

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BobbyZ

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Where you in Park Rapids MN last weekend? Pretty sure 99% of Iowa was here on the 4th.

Anyways there's two electrolytic cap cans I'd replace and any other electrolytic that hasn't been yet. Do that and upgrade to a grounded cord and add a fuse if there isn't one.
Then see how the tubes work.
 

muchxs

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doesn't seem right to me based on my little experience with tube amps.

Don't tinker with it if you don't know what you're doing. It's in "collector" condition as- is. While it makes little sense, "Untouched solder joints and all original parts" are where the value is. It's too bad 'cuz I keep myself in biscuits and sometimes gravy touching solder joints and changing parts.

It has an ancient field coil speaker that will be difficult to repair or replace if you damage it.

That lap steel will sound just as good or better through a low buck Champ clone.

The Champ was originally the companion amp to Fender's lap steel, one of the first "beginner packs".
 

Wally

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Sharp pair, there! PRoceed with caution as muchxs says. The 7C5 is a power output tube. The 7F7 and the 7C7 are the PI and preamp tubes, I'm guessing. Find the pinouts for those tubes if you want to understand the circuit better. Duncan Tube Data is your friend.
Nice find.....kudos.
 

Waikiki model 97

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Manchester nh
Picked up a matching Lap steel & Amp set, Tweed Model #97 Waikiki, Labeled "Chicago Musical Instruments Co" 50 watt , has loctal tubes, 7Z4, 2 x 7C5,7F7,7C7 .
I have it working; I replaced 3 of the paper capacitors and now sounds good but think may still need some attention ? the 7F7 get warm not hot like the ones on the left and the 7C7 does not warm up at all :confused: doesn't seem right to me based on my little experience with tube amps. I can not find a schematic anywhere so far. There is one paper cap ( the horizontal one in picture) that I haven't replaced, my tube guy up town wasn't familiar with it, someone mentioned it may be a Power tube cathode by pass cap ? I also read something about the 7C7 being a pre amp tube and it draws very little voltage ? I'm learning as I go, any help on this amp would be greatly appreciated !
I'm probably the leading authority on this particular amplifier, I own four and it's my main amplifier I use. Ask me anything. Can I have your old paper capacitors? Can I buy them off of you?
 

Wally

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Surf's back up and Waikiki is too! Aloha... Waikiki, I figured you were still here and simply waiting for any queries. While we continue to wait for the OP to get back to you with any questions....Are you a slide player? I have a couple of Masco amps that use the 7C7 in the input stage, but they run 2 x 6L6's for the power.
 

Waikiki model 97

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I'm actually a guitar player but, I have given much thought to learning slide. These are very rare valco amplifiers, manufactured from 1942 to 1948. Interestingly, not only are the amplifiers rare but, also the components as well. Probably a rola field coil but the speaker is unbranded as are the transformers. Well, I suppose I should not use the word rare because the transformer voltages are very common.
 

Wally

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The fuse assembly is very unique on this model.

As regards the hot and neutral, the schematic linked to above shows a fuse circuit that is just as most of us use when installing 3-way power cords to old ungrounded amps or even the early 3-way power cords in SF Fenders....one AC leg through the fuse to the switch to one leg of the primary while the other leg of the AC supply is wired directly to the other leg of the PT primary.
 

mdyhrkopp

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Iowa
I'm back....I sold the old Waikiki and am currently Restoring an old Harmony model 200, I also have a mid-late 1930's Oahu that I can find no schematic either for, and previous owner and one other re-wired some and changed out most caps, i changed out the others and also some resistors and had the field coil speaker re-coned. It has a hum at idle that I would love to make go away, I have been told its an early pre 36 model 230K hence the old chimneys. I think it may be the same as an older Kay model 859 as I found a picture of the inside of the Kay 839 and it looks like same chassis,trannys,tubes,ect...so a schematic for that may help as well. i posted a gut shot of mine as well as the Kay. Thanks all for great group !
 

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mdyhrkopp

TDPRI Member
Joined
Jul 6, 2015
Posts
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Location
Iowa
I'm probably the leading authority on this particular amplifier, I own four and it's my main amplifier I use. Ask me anything. Can I have your old paper capacitors? Can I buy them off of you?
Tube equivalent

7C5 - 6V6
7C7 - 6J7/6SJ7
7F7 - 6SL7GT
7Z4 - close to 6V4/EZ80 but with 100ma


Tube pin out

http://www.harpamps.com/premier/Model50_7c5_7c7.pdf

Should be not too hard to draw out a schematic.
Thank you a bit too late on my end, I was off the grid for awhile; sold the amp to a collector the way it was, and I was off the grid for a bit, but I'm back and running. Now i'm working on a 1930's oahu Amp..
appreciate the schematic man, i will print out and save for the next Waikiki i may find ! Cheers
 

mdyhrkopp

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Joined
Jul 6, 2015
Posts
27
Location
Iowa
Don't tinker with it if you don't know what you're doing. It's in "collector" condition as- is. While it makes little sense, "Untouched solder joints and all original parts" are where the value is. It's too bad 'cuz I keep myself in biscuits and sometimes gravy touching solder joints and changing parts.

It has an ancient field coil speaker that will be difficult to repair or replace if you damage it.

That lap steel will sound just as good or better through a low buck Champ clone.

The Champ was originally the companion amp to Fender's lap steel, one of the first "beginner packs".
Thank you sir, sorry for late reply, i did sell to a collector the way it was,,,Now I have an 1930's oahu that someones been changing out caps, ect and rewiring it, now ive got a "Hummer' on my hands... and no schematic either..lol
 

muchxs

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Thank you sir, sorry for late reply, i did sell to a collector the way it was,,,Now I have an 1930's oahu that someones been changing out caps, ect and rewiring it, now ive got a "Hummer' on my hands... and no schematic either..lol

Thing is these use big chunks of circuits designed for phonographs and old tabletop radios.

It used to be every little town had a man with a van and a plan... and a caddy full of vacuum tubes. You'd call the MWIVAAP, he'd show up at your house and set your old black and white TV, phonograph or radio straight.

Or you could drop it off at his shop. Usually a cluttered shop packed with dusty televisions, phonographs and old radios. And tubes! Tubes everywhere.

Last guy like that around here offed himself when it became cheaper to buy a new VCR at the Wal-Mart down the street rather than repairing the old unit. They hoed out all his stuff and converted his shop into a martial arts studio. Eventually CVS Pharmacy bought the adjacent real estate and bulldozed the martial arts studio. It's part of the parking lot.

To get to the point: Old timers were familiar with the chunks of circuits cribbed from the RCA "cookbook" and the like. A schematic really isn't necessary,

Except:

Speaking for myself, it can be a time consuming PITA to reverse- engineer some old point to point junker. Every so often I get one that doesn't resemble any known circuit and I've seen a few of them by now. It turns into a head scratcher where we need to deduce the builder's original intent. That may be difficult when the builder's original intent has been obscured under decades of repairs.

Although:

A "hummer" isn't too difficult with a few caveats. Some vintage circuits were prone to hum. It was generally accepted because it was acceptable at the relatively low volume levels of the day. Further, many of those old speakers won't reproduce 60hz.

"Transformerless" circuits tend to hum. I've decided there are amps worth messing with and amps not worth messing with. I don't want to mess with transformerless aka "widowmaker" amps.

Field coil speakers were common pre- 1955 or so. If your amp has a permanent magnet speaker and it hasn't been converted properly... it's going to hum.

Normally we'd make sure everything is well in the power supply while maintaining vigilance for other possibilities.
 
Last edited:

mdyhrkopp

TDPRI Member
Joined
Jul 6, 2015
Posts
27
Location
Iowa
Thing is these use big chunks of circuits designed for phonographs and old tabletop radios.

It used to be every little town had a man with a van and a plan... and a caddy full of vacuum tubes. You'd call the MWIVAAP, he'd show up at your house and set your old black and white TV, phonograph or radio straight.

Or you could drop it off at his shop. Usually a cluttered shop packed with dusty televisions, phonographs and old radios. And tubes! Tubes everywhere.

Last guy like that around here offed himself when it became cheaper to buy a new VCR at the Wal-Mart down the street rather than repairing the old unit. They hoed out all his stuff and converted his shop into a martial arts studio. Eventually CVS Pharmacy bought the adjacent real estate and bulldozed the martial arts studio. It's part of the parking lot.

To get to the point: Old timers were familiar with the chunks of circuits cribbed from the RCA "cookbook" and the like. A schematic really isn't necessary,

Except:

Speaking for myself, it can be a time consuming PITA to reverse- engineer some old point to point junker. Every so often I get one that doesn't resemble any known circuit and I've seen a few of them by now. It turns into a head scratcher where we need to deduce the builder's original intent. That may be difficult when the builder's original intent has been obscured under decades of repairs.

Although:

A "hummer" isn't too difficult with a few caveats. Some vintage circuits were prone to hum. It was generally accepted because it was acceptable at the relatively low volume levels of the day. Further, many of those old speakers won't reproduce 60hz.

"Transformerless" circuits tend to hum. I've decided there are amps worth messing with and amps not worth messing with. I don't want to mess with transformerless aka "widowmaker" amps.

Field coil speakers were common pre- 1955 or so. If your amp has a permanent magnet speaker and it hasn't been converted properly... it's going to hum.

Normally we'd make sure everything is well in the power supply while maintaining vigilance for other possibilities.
 

mdyhrkopp

TDPRI Member
Joined
Jul 6, 2015
Posts
27
Location
Iowa
Thanks, It does have the old field coil, which I sent in and had re-coned, just trying to figure out what all was removed 2-40 yrs ago by the previous owner.
Good thing is the follow i bought from has a all new schematic drawn by one of those good ole boys, that adds a tone contro, and also a balace pot for the inputs, so if nothing else I can start from sctrach and wire up with the caps,resistors,pots, ect that the good ole boy from Maine suggested doing, the previous owner just gave up on doing the conversion...but i may do it ...Thanks
 

mdyhrkopp

TDPRI Member
Joined
Jul 6, 2015
Posts
27
Location
Iowa
Thing is these use big chunks of circuits designed for phonographs and old tabletop radios.

It used to be every little town had a man with a van and a plan... and a caddy full of vacuum tubes. You'd call the MWIVAAP, he'd show up at your house and set your old black and white TV, phonograph or radio straight.

Or you could drop it off at his shop. Usually a cluttered shop packed with dusty televisions, phonographs and old radios. And tubes! Tubes everywhere.

Last guy like that around here offed himself when it became cheaper to buy a new VCR at the Wal-Mart down the street rather than repairing the old unit. They hoed out all his stuff and converted his shop into a martial arts studio. Eventually CVS Pharmacy bought the adjacent real estate and bulldozed the martial arts studio. It's part of the parking lot.

To get to the point: Old timers were familiar with the chunks of circuits cribbed from the RCA "cookbook" and the like. A schematic really isn't necessary,

Except:

Speaking for myself, it can be a time consuming PITA to reverse- engineer some old point to point junker. Every so often I get one that doesn't resemble any known circuit and I've seen a few of them by now. It turns into a head scratcher where we need to deduce the builder's original intent. That may be difficult when the builder's original intent has been obscured under decades of repairs.

Although:

A "hummer" isn't too difficult with a few caveats. Some vintage circuits were prone to hum. It was generally accepted because it was acceptable at the relatively low volume levels of the day. Further, many of those old speakers won't reproduce 60hz.

"Transformerless" circuits tend to hum. I've decided there are amps worth messing with and amps not worth messing with. I don't want to mess with transformerless aka "widowmaker" amps.

Field coil speakers were common pre- 1955 or so. If your amp has a permanent magnet speaker and it hasn't been converted properly... it's going to hum.

Normally we'd make sure everything is well in the power supply while maintaining vigilance for other possibilities.
Thanks for the Info Muchmx ! It has the stock Jensen 8" F/coil speaker that I had rebuilt as well.. I will keep on trying
 

brians dad

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Mar 16, 2022
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68
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mercer island
I'm probably the leading authority on this particular amplifier, I own four and it's my main amplifier I use. Ask me anything. Can I have your old paper capacitors? Can I buy them off of you?
A blast from the past! I found a bunch of loctals, which are useless unless I can use them for something like building a Waikiki model 97.

Is there any chance that you would be willing to share a schematic with me?

Thanks in advance for any assistance or advice.
 




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