Kay 752 amp - does this sound normal?

Update

I just replaced the power tube with a NOS Tung-Sol, and the amp is considerably cleaner now. It's late, so I wasn't able to crank it and see how it reacted, but it's much cleaner at lower volumes.

It's interesting, though, because it seems as though it's actually a bit crunchier at very low volumes (though not as much as with the other tube) --- say from 2 to 3 (you can't really hear anything before 2 because the volume knob is also the switch). Then as you turn it up to around 4 or 5, it starts to clean up much more. This could be that there's more volume to hide some crunchiness that possibly still exists. In other words, maybe the ratio of proper amp tone to the possibly malfunction-driven crunchiness is higher.

I also can't tell if the amp is louder with the Tung-Sol yet, because I can't dime it yet. But my first impression seems to be that I have gained a bit of volume. We'll see tomorrow though.

I have a NOS RCA rectifier tube coming as well and will try replacing that next. If things still seem to be a little fishy, I'll move on to trying out another speaker and then on to the innards if necessary.

But, the tone has definitely improved by replacing the power tube, which gives me some hope.
 
Second update

My rectifier tube should be arriving today, but last night I decided to open the amp up and take a look anyway.

Holy crap ... that thing was a jigsaw puzzle to get open! I remember having a similar issue with my old Gibson GA-5 Skylark. It's not at all a simple matter of unscrewing some screws and the chassis popping out.

You have to first take off the speaker baffle board (the easy part) and then disconnect it from the chassis. That turned out to be a huge pain in the ass because one of the 2 nuts was stripped. I ended up having to cut it off and will have to get a replacement nut. Luckily, the screw seems ok still.

Anyway, after that, and after a bunch of swearing, looking into crannies with a flashlight, and swearing some more, I finally realized that the chassis was two separable parts. Once I realized that, I figured out how to separate them.

If you look at the pictures in alphabetical order, it should be evident I think. Basically, it boils down to this:

The bottom half of the chassis is connected to the cabinet with two bolts, which are inaccessible at first (once the speaker baffle is removed). The top half of the chassis (which houses all the components) is only connected to the bottom half of the chassis via four supporting bolts (the big hexagonal-shaped things). It's not connected to the cab at all.

Once you get the nuts off those four big hexagonal bolts, you can separate the top half of the chassis (which takes a little effort), and then it just slides out from the cabinet. It's just sitting in a tight-fitting groove basically.

Then, once you have the top half of the chassis loose, you can get to the two bolts (see picture F) holding the bottom half of the chassis to the cabinet (if you need to). However, there's not really a need, because almost all of the components come with the top half of the chassis.

The one exception is the cap can (which you can see dangling in picture B). It won't fit through the hole (see the blue and red wires in picture C) in the bottom of the chassis --- at least not without removing its little metallic collar that's tied to ground (which I haven't tried to do).

At any rate, it doesn't seem that it's going to be a walk in the park to replace any components because, even with the top half of the chassis separated (which isn't shown in any pictures yet), I don't think the components board can be separated from those hexagonal bolts. Or at least, it didn't want to give easily. It was late by the time I finally got the chassis separated, so I didn't spend much time at all on that. Maybe it will be doable, but I don't know yet.

I don't think it will be impossible to do anything even if the board won't come loose, but there certainly won't be much elbow room in there. We'll see.

Oh, and I also measured the 6.5-inch speaker, and I'm getting 3.2 ohms. So I'm guessing it's a 4 ohm speaker.
 

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Thanks for the update man, and the detail!

I suspect that the exposed thread+smooth standoff (between board and bottom-chassis) would need to be gripped and unscrewed from the large hex-standoffs to free the board.
Those hex things are, as far as I know, usually internally threaded at both ends so, if you put a spanner on one and turned you'd always be tightening one end and loosening another.

How does the other end of the hex jobs fit to the upper chassis? Are there fixed threads on there?

I like that you swore at twice. I usually find that helps! ;)
 
We can also see that the speaker has large spaced ribbing - suggesting it may not break-up without power ?
 
The good news is that the 8-inch speaker in my Tweed Champ (Weber) clone is 4 ohms, so I can test it out.

I plan to spend some more time this weekend with the amp opened up, now that I know how the puzzle pieces go. :)

---------- Update ----------

It's also really strange about the 6-inch speaker that's in there. The 1966 Kay catalog mentions an 8-inch speaker, and so does the parts list in the amp.

Yet the speaker looks pretty original to me.
 

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Thanks for the update man, and the detail!

I suspect that the exposed thread+smooth standoff (between board and bottom-chassis) would need to be gripped and unscrewed from the large hex-standoffs to free the board.
Those hex things are, as far as I know, usually internally threaded at both ends so, if you put a spanner on one and turned you'd always be tightening one end and loosening another.

How does the other end of the hex jobs fit to the upper chassis? Are there fixed threads on there?

I like that you swore at twice. I usually find that helps! ;)

Yeah from what I can tell, the hexagonal jobs are fixed to the upper chassis. I can't see any threads at all.
 
Ok. If those are welded or permanently fixed then I guess the circled part would have to unscrew?
Might be wrong but I'm thinking it's a spacer/riser with threaded bar on both faces...

circle.png
 
I think you're right that they are spacers. I don't know if that bottom circle part unscrews or not. I'll take a look at it this weekend and let you know.
 
Yeah I don't think it can be removed from the chassis. I was just hoping I could separate them from the board so I have some room to work.
 
It's really hard to tell but it looks like there might even be a crush washer underneath the board in picture F.
If there is then that'll certainly separate.

I mean...surely it has to one way or other. There's no way that boards going to be permanently mounted between two metal plates!?
 
These are are probably the most common types of standoffs I had in the parts bin. One more type may have threaded studs on both ends. Can you see how the standoffs are affixed to the side of the top chassis towards the jacks and pots? I'm almost thinking the bottom chassis may pull off the standoff studs if all the nuts are removed. There appear to be possibly round spacers between the bottom chassis and the circuit board.
 

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Old Silvertone amp.... Schematic and parts list glued to inside of case states 8" speaker. Cone diameter measures about 6" :) Might get 8" if measured to the extremities of where the mounting holes are.
 

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These are are probably the most common types of standoffs I had in the parts bin. One more type may have threaded studs on both ends. Can you see how the standoffs are affixed to the side of the top chassis towards the jacks and pots? I'm almost thinking the bottom chassis may pull off the standoff studs if all the nuts are removed. There appear to be possibly round spacers between the bottom chassis and the circuit board.

The bottom chassis definitely does pull off once I remove the nuts. I did that last night. However, the circuit board did not come off the stand offs. I tugged at it a little (not too hard), and it certainly didn't want to come off easily.

I'm going to get into it again this evening, and I'll try to take some more pictures with the chassis separated into its two halves.
 
Update 3

Ok, so I learned a good bit tonight. I got the top and bottom chassis separated and got pictures of that.

Then I removed the cover panel from the top chassis. See picture E). Notice how there are still nuts on the jacks and pots. There were another set of those holding the cover panel (i.e., the external panel with the amp name and "Volume," etc.) on.

At that point, I finally saw how the hexagonal spacers are connected. See picture F. They're screwed in from the other side. (Seems as though Arcaxis was on the right track.) The one issue is that I can't get the screws to budge. I put some muscle into it with a screwdriver and gave up for fear that I'd strip them.

However, the good news is that, after freeing everything up like this, I do think it will be workable without removing the hex spacers. The board isn't very deep at all, and with being able to get at it from both sides, I don't think it will be too much of an issue to do anything. The main thing is that I have complete access to the bottom (soldering) side.

Now that I have it completely open, I'll replace the power cord with a 3-prong.

Interestingly, none of the electrolytics look in bad shape. I don't see any bulging at all. Also of interest is that a few of them (there aren't that many in the first place) are different values than shown on the schematic. This makes me think that maybe this amp has had a cap job and that the original values couldn't be located?

One more thing I noticed was that this board was obviously designed to be used with a preamp tube circuit, as can be seen in pictures G and H. The connections are all there; they're just not being used at all.

This made me wonder how hard it would be to modify the amp to use a tube input stage instead of the transistor. It's obviously not going to use a 12AX7 or anything like that, because it's a 7-pin tube socket. Maybe something like an 18GD6a? That's what the Kay 703 uses for its preamp tube.

Anyway, any thoughts on this Arcaxis?
 

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So I replaced the power cord with a 3-prong one, but to be honest, I'd be lying if I said I really understand why it’s necessary. I’m hoping someone here can shed some light. Let me preface this by saying that I’m not trying to be a smart ass or difficult; my questions here are truly sincere.

I certainly have plenty to learn about amps. I know enough to have built two of them, and I know to discharge them before working on them, etc. And I haven’t been shocked yet. But what I don’t know could still fill a landfill, and I’m reading up on it to try to learn what I can. But it’s not coming easy for me. Music theory? That made sense to me right away. But electronics is a bit harder for me to grasp. Anyway, I digress.

I’ve heard all kinds of things about transformerless amps --- people call them “hot chassis amps,” “widowmakers,” etc. I’ve heard contradictory things about “death caps” --- you should remove them; you shouldn’t remove them, etc. But I really don’t understand this all.

I’ve heard many people say things like, “If you plug (an amp like my Kay) into an outlet and have the two-prong oriented the wrong way, you could have full voltage on the chassis!” You could have? What do they mean could have? Wouldn’t it be yes or no?

People make it sound as though you have a 50/50 chance of being lethally (or fatally) shocked with these amps because of the above statement.

But I’ve plugged the Kay into numerous different outlets in the house since I’ve owned it, and I have no idea which way the plug was oriented (there’s no way to tell because one’s no bigger than the other). And I haven’t been shocked yet. (Because of all I’ve heard/read about these amps, I always do a little test by just bouncing the back of my hands quickly off the strings before I fully commit to playing, just to make sure.)

Have I just been lucky and had the plug oriented the right way every time? That seems unlikely.

Are all of these horror tales only applicable if the amp circuitry fails in some way---like some kind of short? Because many people don’t make it sound like that.

Does anyone personally know anyone or know of anyone who has been shocked by one of these amps? And if so, what was the situation?

So … in the words of Denzel Washington in the movie Philadelphia, “Could someone explain this to me like I’m a six-year old?” I’m trying to understand it, but I can’t wrap my head around it yet.

I really appreciate any help I can get!

BTW, here's a typical post like the one I'm referencing. This comes from a topic on TDPRI.com called "Transformerless Tube Amps."

A buddy of mine has an old Epiphone Electar (pre-war) that he restored that has no PT. As pointed out in describing one similar to this (Electar): "The plug was non-polarized. Meaning, every time the amp was plugged in, there was a 50% chance the chassis would have 120 volts on it."


This can not be true. Can it? There's no way that Epiphone would be releasing an amp that would shock the hell out of someone 50% of the time. They'd be out of business in a month, as would any other manufacturer who did the same.

Or maybe I'm misunderstanding how you'd get shocked in those situations. Would you need to be playing barefoot in a damp basement or something? Would you technically be ok if you were on carpet in the second floor of your home, even if there were 120 volts on the chassis?

I told you .. I still have a lot to learn! :)
 
in a word its case ground for "safety".
the old two prongs were only about getting AC to your circuit. the third prong a safety case/casing ground.

in most homes and normal wiring the two ground plugs, of the three prongs, end up at the same place in the panel. thats why when you put a multi meter on the two "ground" prongs in the house receptacle its 0 ohms and zero volts on the multimeter. one prong is hot obviously.

as i read it once- the example was a simple home bread toaster.
Imagine a scenario when the live hot filament in toaster opens/breaks. The hot-ac live side of the broken filament touches the internal metal casing and the toaster casing would get hot and could cause fires or shock someone.

So they grounded this internal case which means the case is grounded. So if the AC should somehow make contact with the metal case it should go to ground not the human and not sit there getting hot and hotter. Going to ground it will trip a breaker (or blow a fuse) because the voltage shorts to ground meaning resistance drops to 0ohms. (this means current skyrockets as resistance goes to 0 ohms = circuit breaker trips due to over-current of circuit breaker ...ohms law).

if I recall the extra-ground was all started when electric devices started filling the homes and fires and shocks were then avoided by having "case ground".
 

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