I think it would be a very big step to try to understand "Logic IC's" from the start.
There are several websites to learn from, and also many books and information on the NET that can guide you on the subject. Texas Instruments have some good info but it might get complicated very fast.
I would start here : https://learn.sparkfun.com/tutorials/digital-logic/all

The first picture shows you have a +4.8v supply that goes to 4 IC's (IC-301 to IC-304)
Pin 14 on the IC's is the positive voltage supply pin (Marked VCC)
Pin 7 on the IC's is the negative voltage supply pin (Marked GND)

In schematics VCC is often the marking for the positive supply, GND is the ground or 0V supply and finally VDD is often the negative supply.

So basically it just shows you have +4.8 volts to pin 14 on those chips and 0 volts on pin 7.

The second drawing you did is of IC303 (SN7472), it is a block diagram of its function, that IC is a "AND GATED J-K MASTER-SLAVE FLIP-FLOPS WITH CLEAR AND RESET".
What that means is that that is the very deep end of the pool for you where headaches lurk, you can try to understand it by reading up on it, I do and it gives me a headache even thinking about it.

All of those logic IC's have modules in them, and the modules are drawn with different symbols that indicates what they do, if you deal with them often its easy to follow but its been to long ago for me to try.

You might not be able to get the exact replacement part for all those IC's but there are many other chips that can do the same function with slightly different part numbers.

I found this page with lots of info on other model oscilloscopes, but not your one.
It is possible they might have very similar schematics or even the same.
Have a look :
https://www.vintage-radio.info/heathkit/index.htm

and just as I was going to press "post" I found these photos:

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It's best to open the pictures in a new window, or download the link when on the small pictures.

Heathkit Cross Reference:
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Whats the model of the Scope ?

Quote from: saturated on October 01, 2023, 02:52:19 PMon my to do list...need to build a curve tracer and connect to my oscilloscope

I don't know if you have a transistor tester yet, but a modern one can be a great item to have, for very little money you can pick up something that can do some amazing measurements on components.
I bought one several years ago but I think I need a new better one as they get better so fast.
I bought one without a case but then ended up buying a case many years later so the final cost was the same as one with a case in the first place.
The old one I have now is in this video on you-tube, the one on the right.
It would be worth spending some time and finding a very cheap one that can do everything the more expensive ones can do, just have to keep looking till you find one.

https://www.youtube.com/watch?v=-pEmM0Kt2UY

Cheers
Mick
 PS...If you find a great cheap one ....let us know

I could not see the schematic, so I will post the ones I have if someone is interested.
Photos would be very nice.You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.   

while I got you here I am really struggling with trying to understand how to be safe with oscilloscope grounding.
I was going to put a two prong adapter on the cord to unground it but maybe that is not a good idea.
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It has been a long time since I used my scope, and my scope is a real CRO.
I usually use one ground clamp that I attach to the 0v rail, as long as the 0v rail is grounded.

All my probes have a removable ground wire so all I am left with is the probe itself, I leave one probe with the ground wire attached.
My old "cathode ray oscilloscope" is nothing like the modern units most people have today, turn it on, have a cupper, use it.

What model are we talking about ?
I have only one Mark Bass service manual, the Little Mark 2.

I have had a good look for this schematic but i can't find one either, are you going to repair this one yourself?
I think this might be a very simple circuit as they sold very cheaply when they came out, it might not be hard to trace out.

If you can open the amp up and take photos of both sides of the PCB we might be able to trace it out for you, the more pictures the better.

I would imagine this might be a good project for people to build and also it sounds ok for a small amp, it might even be ok as a small stomp box size practice amp that you can plug into a speaker cab.

Cheers
Mick

These might have them,

https://www.esr.co.uk/components/transistors.htm

I think the BC337 would be ok as well

The biggest fault with dishwashers is that something small gets in the drain pump and jams the impeller, just remove the item and it's all good.

The second biggest fault is that someone uses normal dishwashing detergent in them and they over suds and then overflow, this causes a small float switch under the machine to cut the machine out, and usually the drain pump runs all the time.
This happens a lot when people have had a party and some good samaritan decides to load the dishwasher and start it for you.
The best way to kill the bubbles is to add some hair conditioner into the machine, it works really fast and that's what most Hotels do.

I once did a house call and found the drain pump blocked, I stuck my hand into the dirty water and I pulled a used hypodermic needle out of the drain pump. I was not impressed.
Another time I stuck my hand into the dirty water and found they had filled it up with hydrochloric acid to try to unblock the machine, that burnt.

BC184, 184B, 184C are nearly the same but their Hfe values are different.
Hfe is basically the gain factor of the transistor, you want to put in what you take out.

BC184LC has the legs in a different configuration so if you put one in the same as a BC184 is in there it will not work.
BC184 has the legs CBE and the BC184LC has the legs ECB.

You should really get the closest matching BC184 you can get for TR1 and TR2,
I used some 2N3094 transistors when I made some Marshall 12w amps.

You can still get the BC184 if you shop around, but I would stay away from Ebay and any Chinese sellers just because there are a lot of fakes around.

If you are in the USA you can try Tubes and More.
https://www.tubesandmore.com/products/transistor-bc184-general-purpose-92-case-npn

I have one original schematic, but there are several versions made so numbers might not match.

It might be you have a different style of PCB, possibly an earlier or later version of the same amplifier.
Marshall would release the same model but with several different layouts but basically the same circuit, they did however completely renumber all the components with several new revisions.

If you have the same circuit you should have 2 47nF capacitors in there, C14 and C15.
Can you find 2 47nF capacitors in there ?
Can you find a 25uF capacitor on the PCB ?, there should only be one.

If you can take some pictures of the top and bottom of the PCB I will see if I can trace your version out for you properly, the more pictures the better.
If I can see the top and the bottom and then compare where the traces go to what component it's fairly easy to do.

Cheers
Mick

It looks ok, they need a big overhaul before you would know if they could be saved.
So it's 120V AC in and you can get 0-140V AC out at 3 amps, say 400 watts.
They would be very nice on a workbench, but they would have to be enclosed with a lead for input and a power outlet for outlet voltage if you are not a qualified technician just for safety.

Me, I would salvage them and use them, but I know whats involved having been a licensed electrician since 1980.

The main worry I can see is rust in any steel parts as that might have caused an internal short in the windings, all the rest can be cleaned and inspected very gently.

It might be cheaper to buy  a new unit with the time and effort (and money) it will take to restore them, but I still would.

Mild soap and a toothbrush would be my starting point, some WD40 to loosen up any seized nuts and bolts and slowly pull them apart.
Some electrical cleaner on the electric parts, rub the windings that have been bared for the carbon brush to run on with something slightly abrasive, you can get stones made for polishing up commutators in motors that are perfect for that.
(I often clean contacts with an eraser made for ink, especially old PCB's before soldering)

Reassemble and bake in an oven to remove moisture and test the insulation with a HV megger, all done.

I would say they are too far gone, but when I zoomed right into the copper windings it looks like the varnish is still good.
They look like nice rheostats that might be ok after a full restoration, but it depends on the metal having survived in the core.

If they clean up ok they could be re-dipped in varnished then tested too se if they are ok.

Rheostats are very useful for bringing up the mains voltage nice and slow when testing electronic gear.
I have a small one and a large one myself.

What are the ratings on them ?

I would guess its in the first couple of transistors in the preamp, TR1 TR2 TR4 TR5 is the most likely in my opinion.

It would be easy to see if it is in the power amp or the preamp, if you turn the gain up all the way and leave the volume pot really low do you have distortion ?
If the amp distorts at low volumes  then it is being generated in the preamp, if you get a clean signal with full gain and low volume then its most likely distorting in the power amp section.

The preamp section goes up to the volume pot, and the power amp starts on the output of the volume pot, C18 is the first component in the power amp.

Cheers
Mick