Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - galaxiex

#46
Amplifier Discussion / Re: Kasino Concert 120
October 26, 2018, 10:30:24 PM
Possibly Q1,Q2 are the source of your hiss.
IDK, just a guess.

Can you read the numbers on the actual transistor, not the Kustom numbers from the schematic.

Those 739 op amps are obsolete. check here...

https://www.ssguitar.com/index.php?topic=1605.0

Also check voltages as per the schematic.

Report those please.
#47
Amplifier Discussion / Re: Kasino Concert 120
October 25, 2018, 09:15:40 PM
Great, you found something.  :)

Yes, probably the left preamp board.

Can you give us a good,clear, in focus picture of that board, both sides if possible.

Also a schematic would help.

The hiss may be a part dying, or just poor spec, noisy transistor(s).
#48
Amplifier Discussion / Re: Kasino Concert 120
October 24, 2018, 08:39:20 PM
I have a Kasino PA head that had an intermittent reverb.

Thumping the cabinet would make the reverb work.

It was a simple bad solder joint. Simple, but not so easy to find.

I suggest the chopstick method.

Pull the chassis and power up and take a wood chopstick and wiggle, tap,
and probe wires and components with the chopstick until you find the loose/bad connection that causes the hum.

Be careful in there with the live circuit.

The hiss may or may not be related to the hum noise.
#49
The Newcomer's Forum / Re: Old 70's Randall Amp
October 11, 2018, 09:34:55 PM
Well if it's not a CMI product,
they at least sourced their chassis and PC boards from the same place.

Lots of other design similarities, front panel and knob type to mention 2.

Thanks for the pics. :)
#50
The Newcomer's Forum / Re: Old 70's Randall Amp
October 11, 2018, 12:02:19 PM
Quote from: that0neguy on October 11, 2018, 11:50:01 AM
Quote from: galaxiex on October 10, 2018, 10:08:32 PM
Quote from: g1 on October 10, 2018, 09:56:32 PM
How about a pic of the front panel showing control names.

And the rear panel.

That amp chassis looks suspiciously like a CMI product.

Very similar to some Gibson SS amps from the 70's.

Also, what's up with those 2 loose lock washers just laying there?
Right by the power switch!!!
First pic, second set of pics.

Actually those washers are in all the pics, just more obvious in the close-up.

Whoa! After comparing pix of yours to mine... the similarities are too great.  Maybe Randall were making amps for Gibson at that time, and simplified things by using the same design.  I'm speculating, of course.  I was just a tot back then, soiling my Pampers.

I did remove the washers, seeing  how they could cause more problems.

Actually... I think its more a case of CMI was making amps for a number of brands,
Gibson, Randall, etc.

Does your back panel have CMI on it anywhere?
#51
The Newcomer's Forum / Re: Old 70's Randall Amp
October 10, 2018, 10:29:57 PM
Here's my Gibson G70

Pretty similar... no?

I bet yours is a Gibson G-90, or maybe a G-100 or G-120

just re-branded Randall.

#52
The Newcomer's Forum / Re: Old 70's Randall Amp
October 10, 2018, 10:19:33 PM
Also, I bet those are Centralab pots.

Pull one and I bet it says Centralab on the bushing right under the threads.
#53
The Newcomer's Forum / Re: Old 70's Randall Amp
October 10, 2018, 10:08:32 PM
Quote from: g1 on October 10, 2018, 09:56:32 PM
How about a pic of the front panel showing control names.

And the rear panel.

That amp chassis looks suspiciously like a CMI product.

Very similar to some Gibson SS amps from the 70's.

Also, what's up with those 2 loose lock washers just laying there?
Right by the power switch!!!
First pic, second set of pics.

Actually those washers are in all the pics, just more obvious in the close-up.
#54
The Newcomer's Forum / Re: Stripboard woes
August 29, 2018, 07:35:17 PM
Must be poor quality.

I have soldered/de-soldered on old Japanese circuit boards in cheap 70's "throw away" type amps
and have seldom had an issue with traces lifting or breaking.
They made 'em good.

That said, some old circuit boards will lift and break traces if you look at them wrong.

Modern strip board that lifts/breaks traces that easy, must be poor quality.

I'm not ham-fisted when it comes to soldering, but I'm not all that gentle with soldering either.

What boards are you buying and from where?
#55
Updated the schematic.

Reason for this update....

With amp volume at "0" and guitar volume turned up, strum guitar and you could hear quiet distorted sound thru speaker.

Spent some time trying to track this down.
Even if I lifted vol pot wiper, signal still got thru to the power amp.... somehow...

Kept on playing with the circuit and trying different things...

Discovered that if I lifted one end of C17 coupling cap to reverb Q4-Q5 drivers, problem went away.

Ah HA!!!
Signal at Q4-Q5 was modulating the power supply.

Added power supply filtering/decoupling.
R 36-37-38 and C 24-25-26

Makes a HUGE difference!

Amp plays waaaaay cleaner and louder!

I have heard (read) that the power supply is the most important part of an audio amp.
This lesson really brings that home.

Not something I will soon forget.

I was going to post asking for help with this, but finding out, learning on my own, really makes it real.  :dbtu:
#56
If you have time, maybe have a look thru this place.

https://www.surplussales.com/ShaftHardware/Knobs/Index.html
#57
This is for a Super Tramp but might help with the switching.
#58
The Newcomer's Forum / Re: Centre Negative DC Jack
July 03, 2018, 07:14:34 PM
Quote from: nosaj on July 03, 2018, 10:52:12 AM
Nevermind they sell them
https://www.musiciansfriend.com/accessories/truetone-reverse-polarity-converter-for-1-spot
nosaj

Boy, I'd be marking THAT with some kind of bright orange or yellow tape....
#59
Sounds like a bad cap somewhere.
#60
Tubes and Hybrids / Re: Tube shields on EL-84's
May 07, 2018, 11:37:30 PM
No, actually the sockets are very tight.
It's a bit of a struggle to pull them.
I do use a rocking/rotating motion to remove them.

I suppose I just liked the idea of retainers since they do hang upside down when in use.
I'll not bother with these, if my OCD nags me into retainers I'll get the wire type.