Guild 98-RT pics

boss55chevy

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Hi guys,

I'm chipping away at putting the 98-RT back to functioning order. It's missing the back panels, and footswitch. (and logo) I may never find these items. So I may have to fabricate the back panels for now. Any images of your own 98-RT would be greatly appreciated. Fram a few angles too. You can also email the pics @; boss55chevy@yahoo.com Thanks so much.
 

capnjuan

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boss55chevy said:
Hi guys, I'm chipping away at putting the 98-RT back to functioning order. It's missing the back panels, and footswitch. (and logo) I may never find these items. So I may have to fabricate the back panels for now. Any images of your own 98-RT would be greatly appreciated. Fram a few angles too. You can also email the pics @; boss55chevy@yahoo.com Thanks so much.
Hi Chevyman and welcome to LTG. If you are as handy as your post suggests, then you know that any footswitch with single pole switches will work and .... very good luck on the logo. If you get a moment, why don't you post some pics of what you do have ... chassis shots especially appreciated. Again, welcome to LTG! John
 

matsickma

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Here are a few pictures of a early 1960's model I had a few years back. The extra speaker connection on the back of the amp is not stock.

1front.jpg


2back.jpg


3top_wFootswitch.jpg


4controls.jpg


M
 

Brendan

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I want one of these. Anyone know what the going price is these days?
 

boss55chevy

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Hey matsickma and capnjuan, thank you!!!

Great pics! Mine is of the variety with the gray pebbley covering with a leather handle, but otherwise the same. After sitting all these years it fired right up. I took out the chassis and had to replace about 6 wires. In the 70's my band used to rehearse in an old house my Father let us use on our farm. The house had heat. electric and MICE! We were using other equipment at the time so the 98-RT just sat there for weeks at a time with no one being in the house. Upon moving the amp back to my own house I noticed that the mice tried to inhabit the 98-RT. But more disturbing was that they ate some of the insulation off some of the wires. but, get this.....only the WHITE WIRES. So for now I spliced in good wires as 'point-to-point' as I could w/o possibly damaging the board by being too aggresive. It fires up, plays with the normal cap noises we're all used to. It's really a keepsake so it's fine the way it is for now.

Does anyone know if the pebbley covering and leather handle is slightly older?

Thanks everyone!

B
 

boss55chevy

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PS I'll get my Daughter to take some shots of it to post. (i can be technologically challenged at times, I don't own a digital camera :)

B
 

matsickma

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Yes. That type of tolex was used around late 1958 to early 1960. Does your amp have a square or trapazoidal front speaker baffel. If it is square and grey pebly tolex it is later in the series just before the grey tolex model I posted. The picture shown below is a 40T amp with the tolex you described. The front grill is trapazodial implying it is a year or two earlier than yours. The second picture below is of a 100J. This is the style Guild used on its amp starting around 1955/56 when it issued the new models: 50J, 66J, 99J, 100J and 200S. Prior to this period Guild had a variety of Masteramp models.


Picture202.jpg


1GUILD_FRONT_100J_AMP.jpg


M
 

boss55chevy

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I THINK this will work. (If not maybe they can be copied and pasted) The speaker was just purchased from ebay (a little more correct) Note the the covering chewed off the bottom front (thanks Happy! My dog from the early 70's) and besides mice chewing some of the wires while in storage, they also chewed or ate the peper labels off of some of the caps/resistors etc. Thanks for all the help guys. (see the missing logo, back panels and footswitch)

B

[img]http://i396.photobucket.com/albums/pp42/boss55chevy/3abce4c1.jpg[/img]

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[img]http://i396.photobucket.com/albums/pp42/boss55chevy/cb3b81fc.jpg[/img]
 

capnjuan

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Congratulations Boss; apart from cosmetics, you have yourself quite a bit of usable amp there! J
 

boss55chevy

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Thanks Capn'. Here's the real cool part of the story. Christmas '62 my parents bought me a Kay guitar and amp set up. Well on Christmas morning the Kay was DOA. Not a peep. (knowing what we all know now it was probably a cable or something simple at worst) My parents had a farm, a store, greenhouses etc etc so they really couldn't get out to shop much. So after the holidays the guy from the music store brought out a bunch of stuff for me to look at and a try out to replace the Kay. In that stuff he brought was this (used) amp and a new Strat which I still have as well. Through the 60's and early 70's I used to trade them for other equipment then get them back. This happened several times until I realized I better hang on to them. So I did, and I'm now getting around to putting them back into near correct condition. I have to thank you guys for the help, so thanks!

B
 

capnjuan

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Are you going to do the electronic work or take it somewhere? I can tell you that it needs at least a 3-wire power cord and new power supply filter caps ... or a fresh can cap if you can find it ... the shiny thing second from the far right ... not sure what that is on the far right ... got a close up? Fairly rare Guild-badged speaker ... probably a CTS ... can you give the speaker code on the rim? 137 XXX is CTS but could be something else. If you don't have a schematic, this guy says you can have one of his for $5.00. Twin 6SL7s and twin 6SN7s in the preamp ... twin 6V6s, 5Y3 rectifier ... can't beat that! John
 

boss55chevy

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Wow, you know your stuff. I could handle the hands on part (soldering etc) but I wouldn't know what components to change, their values, polarity sensitive etc. (that's for you real techs know) I'll get more speaker info later. (a better pic might not be doable) I'll change the line cord next time I play with it. Thanks for the info! It means a lot.

Barry
 

capnjuan

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Hi Barry; my first suggestion would be to buy that guy's 98RT schematic. If you can, scan it and email it to me. Take some clear, close-up pics of the circuit board - left half, right half - and between what's in the amp and what's on the schematic, we can tell you what needs to be replaced.

Also; need to know the diameter of that multi-section can cap (next to far right) and how many hot sections it has - can be determined by looking at the bottom of it. There will be several terminals maybe with resistors mounted .... or you can take pic but the # of sections and its diameter will determine whether the aftermarket has a drop-in replacement for you or not.

After the cord, the can cap is next priority. After that, you'd be after the several electrolytic caps - brown cardboard cylinders - on the ciruit board which are the cathode bypass caps, and the several caps that make up the tremolo/oscillator circuit that normally need to be replaced. In this amp, there are no caps whose + end are connected to ground; provided you can distinguish which end is ground, all the electrolytics will be mounted - to ground. Anyway; first things first ... schematic and sharper pics. John
 

boss55chevy

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Awesome, Thanks John. I'll get on that and get back to you. Thanks for all the help.

B
 

boss55chevy

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Hey Cap,

*Here's the #'s around the outside of that Guild speaker: 137433 5812071 018001

*The aluminum can to the right is about 1.5" in dia. It has 4 contacts w/a good size resistor across 2 of them.

*There's also another aluminum can (that was dangling) to the right of the larger one. It has 3 wires going to it and is about 1" in dia. (I fashioned a bracket and secured that one)

*At my work computer I have a schematic, I'll send it tmw.

I was wondering if anyone out there had either a 98-Rt, J66 or other model with the same logo that wouldn't mind spending a few minutes jotting down the demensions of the screening size, plate size etc. I can reproduce one with some simple coordinates. Thanks!
 

capnjuan

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Hi Barry; the speaker is a CTS and probably original - that badge is pretty cool. If the voice coil or cone are shot, worth the $40 (cone) - $75 (cone and vc) to get it repaired. The can cap: you can look here: Mojo Music Supply, Antique Electronics, WeberVST, and Hoffman Amps. The values for the separate sections will be printed on the side; 20/20/10/10 ... whatever. If you can't find a conventional replacement, Weber sells Electrolytics in a variety of configurations in colorful anodized aluminum cans. Sold for kit-builders and not necessarily restoration, they look like this (that's Coastie's T1 RVT showing off including relocated fuse post that can be reached without pulling the chassis :evil: ):

tubedeckB.jpg



Any chance the next-to-right is 1 3/8" at the top ... not at the lip where it meets the chassis? If that right-most can cap was never fastened to the chassis, then it's an effort to either to overcome a failing original or add capacitance to improve performance. At the end of the day, if you find something that matches the original design, that thing ought to go bye-bye. Looking forward to the schematic! John
 

capnjuan

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Hi Barry; I've been reviewing the 98RT schematic in anticipation of your rehab work; hope this helps. All the images Here.

Reference Schematic:

schematic.jpg



Reverb:
The reverb signal is taken from V1A (left half) downstream of the tone and volume controls and is fed (magenta line) to the grid of V2A (left half). For the time being, ignore the dotted red line and follow the magenta line as it heads to the grid of V3A - the reverb driver - where it is amplified again and is coupled to the reverb can by a .22 capacitor; this is an Ampeg design feature. After it comes out of the reverb can, it sees a switch - red oval - connected to ground. When the reverb is switched off, the signal coming out of the reverb can is grounded out. The reverb signal - if on - is recovered by V3B - reverb recovery - and is re-amplified.
reverb-1.jpg

If the switch is in the 'on' position, then the 'verbed signal - the light blue line - is returned to the signal path at the grid of V2B where it is mixed with the dry signal. The signal, dry if the reverb is off or wet if on - the olive line - now boosted by V2B continues to the phase inverter / driver and appears at the grid of V4A and out via the 6V6s. The dotted red line - a 22K resistor - couples the two V2 sections together and assures that if the reverb is switched off, there will still be a dry signal which is fed to V2B at the cathode. As with the tremolo, all the passive components of this circuit are subject to load because everything ahead of the footswitch is always on.


Tremolo:
The power for V1B - the tremolo oscillator - is taken from power supply tap 'Y' and appears on the plate of V1B. The function of the tube half is to generate pulsing DC power as set by the speed and depth controls. The line signal never passes through V1B; it's output is applied to the 6V6 grid bias resistors. When the switch is on, the grid voltage of the 6V6 swings up and down causing the volume to go up and down according to the control settings and causes the oowaaoowaaoowaa ...
tremolo.jpg



Stage 1:
Caps on the left: V1 is divided between preamp and controls functions and tremolo. Each 1/2 has its own cathode bypass capacitor the contributes to the tube half's bias, gain, and frequency response. For whatever reasons, V1A has a 100uf bypass cap [C5] and V1B has a 25uf cap [C1] a common value. Both need to be replaced. The tremolo circuit has three .05 caps [C2-C5]. The failure of one or more of these caps that are always on is the primary cause of no/low tremolo. If it were my amp, I'd replace them whether they worked or not. C6 is a coupling cap; my inclination is to replace but it's your choice. The tone caps are shown in the blue circle. They are normally mounted on or between the volume and tone controls and not on the circuit board. If they aren't defective, I'd leave them alone. Finally, there's a coupling cap identified by maroon circle and a Question Mark. The missing value is a drafting error, likely to be anything from .01 to .05; whatever it is, it'll be the only one at that end of the board that hasn't been identified so far.
Stage1RsandCs.jpg

Resistors on the right: The grid stopper and leak resistors shown in the red box are likely mounted on the jacks; they don't do a lot of work and unless you have reason to think one or more is bad, I wouldn't mess with them. On the right, the cathode and plate resistors - identifiable by their color bands but covered up by the caps - they all need to be replaced. The 120K value can still be found, if you have trouble with the 170K, use 150K ... the values are not that critical anyway ... the cathode resistor values easy to find. Finally, that 270K resistor above and to the right of the Speed control on the schematic; he's a worker bee ... he gets replaced.

More as I get the other sections finished. John
 

boss55chevy

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Wow Capn'! You're like the mad scientist of the tube amp world. You did a ton of work, Thanks SO much!

B
 
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