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June 25, 2022, 10:12:35 AM

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Need help fixing 2 solid state heads

Started by Mark N, May 12, 2013, 11:57:56 PM

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Mark N

Hey, there,

This is my first post. I recently picked up an old Sears Silvertone 1465 head as well as a Kay 765 for pretty cheap. They need some work. I've built pedals before, so I'm pretty sure it shouldn't be too hard. But I thought I ask here to see if anyone has worked on these before and had any tips or good resources to share. I have read up on draining the caps and other safety hazards. I doubt I'll be ever be working on it plugged in, but any safety tips would be appreciated.

Both are from the late 60's so information is a bit sparse. All I could find on the Kay is an old catalog. It seems like no one ever owned one. I did find the Silvertone Schematics online though. Anyways I was wondering...

1. How do I figure out the fuse type they need? (The Kay doesn't have it written. I know the Silvertone is a number 3) Also how do I know if the fuse is slow blow or instant?

2. How to I figure out the OHMS output for speakers? I have a multimeter, but I'm not sure what I should be checking.

3. Both have 2 pronged outlets that need to be replaced. I also have an old tube Harmony H-415 that needs a 3 prong plug as well. From my understanding, I drain the caps, then replace the plug with a 14AWG, replace the wires as they are and put the ground to the chassis(sanded down if there's paint) with a screw and a star washer so it will never come undone or loosen. Should I solder it as well or is that overkill? I figure it wouldn't hurt.

Any response/feedback/resources and or tips would be appreciated.


I won't be of a lot of help since I am not used to work on amps, but I kinda lurk here to learn helpfull things.

First questions to ask are:
1° are these amps working? If it ain't broken, don't fix it.
2° if they are not working properly, what are the symptomes? Descibe how it reacts to a guitar plugged in.
3° you seem to have the schematics for one of these. Post it here, It will definitively help your case. Maybe start with fixing the amp for which you have the schematics, it will be easier for people here to help you with this one.
4° try to take some quality pics of the board of the other amp, it may help.


Yes post schematics and other info you found on other amp. We need to know what you have there... Basically, the pictures can be priceless too! For example, lets see or read what the ratings are for the main filter caps on the Kay amp. 

Every question QReuCk asked is spot on and is exactly the place we need to start.
"A person who never made a mistake never tried anything new." -Albert Einstein


Prior to answer questions 1 and 2, you may want to have your speaker ohm ratting question answered.
Basically, SS amps are not as selective as Tube amps in this regards. Usually any 8ohm load will do, but you can be pretty safe with 16 also.

J M Fahey

The Silvertone is 100W/4 ohms or around 70W/8 ohms.
The Kay is anybody's guess but since it's "100W music power" which usually means "50W RMS" it should be happy with 8 ohms loads.

As of "needs some working", the *big* question, as Qreuk says: *do* they work (even with scratch/hum/buzz) or not?

Mark N

Thanks for responses! I have not tried them yet because I wanted to know what speakers/Ohms and fuses to hook up before hand.

The Kay:
To start, I was told that they were not working. The guy I bought them from had said that the Kay did work but blew fuses. (I don't know what fuse he has in there and I want to make sure I have the right one before doing any work on it) I had plugged it in without speakers to test if the light came on. . It did. (If it didn't that would mean a problem with the power transformer (aka expensive problem), right? )

The Kay did have power, but also a fickle power chord that was cutting out. I also opened it up and poked around and found that a thick wire connected to the reverb had some tape on it. I undid the tape and found a wire insulated within another wire. The outside wire was not connected to anything. I assume it needs to be grounded. The other wire (which had been modified, probably fixed) goes to the TIP of the input jack for the reverb foot switch and is connected to one end of the reverb pot. The middle of the pot goes to the circuit board and the other end of the pot is the one not connected, (that I am assuming should be grounded) There is also no reverb tank so maybe someone gutted that and just left the wire.

I was told the caps on it were replaced. The looked new and had the price stickers still on them so I believe it to be true.

One reads " CE68
55V 3300uF
The other reads:
55V 3300uf
and I can't read the last line without pulling it out.

The Silvertone: I haven't plugged it in because it is missing the fuse as well as the fuse cap. Also when I opened it up I noticed it is missing a transistor on the 2nd channel. It also is missing the cardboard tube reverb tank that it is suppose to come with. I have a schematic that I found online of the 1465. I do not have it verified, I grabbed it off a message board while I was researching.

As for pictures all, I have is a crappy web cam camera which might not help at all. I'll see what I can do about borrowing a digital camera and snapping some pics of the guts. I understand that makes it a lot easier to see what I'm talking about. I really do appreciate any and all help/advice.

JM Fahley: How did you know the Speaker wattage for the Silvertone? And for the Kay is there anyway to test for the speaker ohms and wattage needed?

Mark N

Also the Kay has 2 output (?) jacks on the back

J M Fahey

Math helps.
+/-35V is *just* enough for 100W/4 ohms because it means 20V RMS=28VPk
to which must be added 3 or 4 V loss at the transistor , 1V across the 0.27 ohm resistor and a few volts to account for PSU voltage drop under load plus a couple V of ripple, which must be discounted too.
For 100W proper it would need at least +/-38 to +/-40V idle (no signal) but oh well, let's forgive them the little hype.
I've seen *far* worse.
As in: if you measure 80 or 90 clean watts, fine, it's *loud* anyway.

A couple 2N3055 can *just* provide 100W into 4 ohms, and if you don't have them, go up, never down.
That's why with that crazy 6x10" cabinet they had to settle for 5.3 ohms ; the option would have been 12 ohms which would have compromised power a lot.
6x10" is an electrically inefficient configuration, but I bet 6 10" cones must move a lot of air so it compensates acoustically.

As of the Kay, it's an educated guess since we have nothing else to work with.

Don't know your Tech skills or equipment, but you'll need both to repair them.

In any case, build a Lamp Bulb Limiter and use it.
Search this Forum.

As of fuses, the Silvertone schematic states a 5 A , standard fuse.
The presumed 50W Kay should need around 3A , similar type.

But anyway the bulb limiter will avoid them blowing while on the bench.

Mark N

If anyone needs an old Kay catalog. It's here:

From the description (on page 10). The Kay 765 head has 100 watts of output power and goes into two 12" speakers.

I have plugged the Kay into some speakers. I didn't get any guitar sounds but I did hear a faint hum sound. So that means the power transformers are good and there's a problem elsewhere.

JM Fahley: The thanks for your help. The Lamp Bulb Limiter seems like it will be useful. I have a question about the Silvertone Fuse type. The Schematic reads
"Fuse 3AG
5 Amp"

And the back of the head reads 3 AMP. I have always been using that suggestions on amps for fuses. What is the reason for the two numbers?

J M Fahey

QuoteI have a question about the Silvertone Fuse type. The Schematic reads
"Fuse 3AG
5 Amp"

And the back of the head reads 3 AMP. I have always been using that suggestions on amps for fuses. What is the reason for the two numbers?
*Maybe* they are using the "Fusing for fools" technique, quite popular in guitar amps.
Wonder why  :lmao:

Fact is, musicians are known for "repairing" blown amps by replacing original fuse with a nail/aluminum paper "turd"/20A fuse pulled from car/motorcycle/etc , often makin amp (and sometimes home or venue) to catch fire.
Insurance companies don't like to pay such claims, so a common practice is to show an external proper fuse (3A) *plus* an internal somewhat larger one (5A).

If you replace external one with proper value, it will *always* blow first, and nobody's the wiser , but if if a never blow type is used, the the internal one does.

Modern amplifiers include a "thermal fuse" **inside** the transformer, so there's no way of bypassing it.

Mark N

I see. So I should be using a 3A then, correct?

Would it ever be necessary for me to switch the internal 5A?

J M Fahey

*If* there is an internal fuseholder ir a fuse wrapped in electrical tape or heatshrink tube, leqave it as-is.
If not, don't worry, I trust you not to bypass the normal fuse with some mad "solution".