Looking around for some info on the Boss Katana Mini, all I could find was this post
Modding the Boss Katana Mini for Rechargeable Batteries

The main ICs are :
TI TPA3131D2 Class D power amplifier
JRC2740 op amps
JRC4580 op amp
PT2399 delay/echo
TI 87 - not sure what this is

Personally I don't find the Delay very inspiring. Maybe they should have gone with an FV-1 instead of the PT2399.

Here's some photos:

P1070569.JPG
P1070572.JPG
P1070574.JPG
P1070596.JPG
P1070617.JPG...

Hey Everyone,

Earlier this week, one of my best friends dropped-off for me at my place an old 80's Tascam M-520 20 Ch Analog studio mixing desk, plus the power supply, this is going to be a fun restoration project for myself because I'm planning on using it in my studio hopefully with my Focusrite Saffire Pro 40, assuming I can get them to play nicely with each other.

Here's a pic of the mixing desk set-up in my little studio room:

I'm building a sort of jcm800 type tube preamp with a master volume right after the cathode follower/tone stack stage. Nothing unusual. My question is do I need a coupling cap after the master volume? This will be the output. I know this is obvious to most of you, but I'm not sure. Any help is appreciated.

I got this head amplifier to repair.
It had issues in protection circuit block.
I searched the net, asked T.E. for schematic, no way....

So I reversed engineered it.
This schematic is the missing part of the .gif I also attached (sorry for the author, I don't know whoever he is...) for archive purpose

So... enjoy it.

VA350 Schematic.pdf

This is the schematic I found on the net.

VA350_diagram.gif

I am going to try to build the preamp section of the Mk I Mesa Boogie. I have found several schematics with some variations. I think I understand how all 4 stages of the 2 12ax7s are switched in for the high gain channel. The query I have is in some schematics Input 2 is shown with a 220k resistor hard-wired to ground. In another, the resistor is wired to connect only when Input 2 is not used, shown in the attached picture. Any ideas on which one is correct please?

I am looking for a schematic diagram of the amplifier Laney LX35D, best regards

How about using an IRF820 as V1, with:

- a 100k resistor between drain and power supply

- a (1k5, xxuF) pair between the source and the ground

as the Mosfet folies document suggests that the MOSFET can be substituted to a triode ; and if so:

- what about an input/gate resistor?

I've already assembled a vintage Vox AC4 inspired amp, as per Merlin The Valve Wizard Blencowe's instructions (the small signal pentode) that is with a triode feeding the EF86 on input.

This lefts an unused...

Got it dirt cheap, completely underestimating the size of the thing.

I did not find any mention online of Davoli Orbach B3 , but it seems to be very close to this Orbach 50

It has an preamp using SN76131N, and what I think is a buffer using a BC109B. The power section seems to correspond to this schematic:
Davoli Orbach power.gif

I did some minor work on it, replacing some exploded caps in the preamp. It sounds amazing, but maybe this is just me learning that I like closed cabs? The only...

Spring cleaning has suddenly brought some tube amps into my life. None of which are specifically guitar amps.

Having never had a vintage tube amp at all I began reading up on theory before I started plugged them in.

I personally primarily value function but honor peoples views on original vintage stuff and understand that there's less vintage original stuff everyday.

One of the amps is a Newcomb E-17 in great shape that came to me in original condition.

Pondering the Newcomb, the fact that...

There is one thing in the ENGL amps that I noticed and implemented in my GXT100 mods:
They use a 330k anode resistor and a 3.3k cathode at about 350v I think.
My goal is to figure out how many fet or mosfet stages one would need to cascade to
achieve a similar distortion quality and compression.
I am assuming something like the Shaka express clipping stages with perhaps one or two more
or a pair of bs170 BOR/SHO type at the tail might get close. I realize that 4 or 5 fets is
considered a limit...

I'm trying to adjust the internal trimmers for the gain stages. I looked up the service manual it says adjust trimmers for 1.4 v on pins 1 and 7 on the opamps. But my voltmeter says 15v it will not adjust to 1.4v any body have any knowledge with these. I was trying to adjust the trimmer on the compression opamp it says 45mv but im getting like 15v on it to. I just bought this used with the foot switch since this is 34 years old i dont know if anybody has messed with the trimmers inside. Just...

hi,
sorry it's a hifi amp request. hope that's ok.
BEL 1001. brown engineering labs.
having a heck of a time finding the schematic.

anyone have a copy?

I had bought this amplifier in the 60 watt version in 1983 defective, the transformer was burned out. I have repaired it in the 1990 years and sold it. Now i have redrawn the very blurred original schematics on a request.
Because the transformer was defective I could not measure the transformer voltages, as far as I remember I replaced it with a Fender compatible one.
I took the shown voltages from the original circuit diagram.
MesiaZoom.jpg
Mesia-60-T_PRE.JPG
Mesia-60-T_PA_60W.JPG...

Hello everyone, I would need the diagram of a fbt jolly 12 RA case or the photos of the electronics to be able to detect the value and position of the polyester capacitors

I posted this on the SS Guitar forum

Well, I just had two more of these abortions in my workshop - both with that nasty buzz/ hum ;)
I tried increasing the capacitor at the input of the 10v regulator but unfortunately the buzz was still there, although reduced slightly, SO, i decided to find out what exactly is wrong with these poorly designed amplifiers and discovered some very interesting crazy design faults.
First : The grounding scheme for these amplifiers is disgusting ! The amplifier...

Hello everyone, first post here.
Calling @modman, found a Geloso G 227A and after fully repaired, want now to mod its one input only like in Bassman. I am planning to add a cathode res in first pre tube (pin 3) 1K and 25uF in parallel to gnd and replace the grid 3.3M with 1M resistor. Do i need to also remove 470K and 22nF and add the usual 68K or it is not necessairy?

Big ups modman for your offer on diy world so far.

So I got this amp, its a Monoprice 15 watt tube amp thats suppose to be modeled just like the Laney Cub12R I think.

I got the schematic for it. I was just wondering if anyone could help me ID this resettable fuse. And where can I find a replacement?

Laney calls it Laney PN 007390
the schematic also calls it PTC6.0

I looked the part up on ebay and found one that calls it a pollyswitch resettable 30V 6A fuse.

Is that what this part is? It was just jumpered when I got it. I want to replace the...

Got a laney cub 10 about a month ago and was very pleasantly surprised by how good it sounded, very full, open,and even the 3d swirl thingy that has to be heard to be believed, in other words, great amp for $200!

Until the trouble started...first the preamp tubes started the occasional sputter, boiling sound, changed them, all is good again. Week later I notice that the sound more unpleasantly distorted than normal, so I back off the master volume by about a quarter turn, the amp actually get...

Hi everyone!

I am looking for some advice here. I recently bought this amp. The brand is called FBT, model 250. It is reported to be from 1977, Italian made. It has a separate pre-amp and main stage.

Main stage has 2x el84, plus 1 x ecc83 (phase shifter?). Preamp with tremolo has 2 x ecc83.

It has two channels. Normal has high and low input, no tremolo.
Guitar channel has high and low input with tremolo. The high input is broken. I need to replace a resistor, jack input and solder again....

Been slowly getting around to learning how to draw load lines and all the stuff related to tube charts but I was wondering how the Klipp circuit on the Laney Klipp amp works. I got an idea how the bypass is executed but I was wondering what is going on in the Klipp tube stage that creates the hybrid fuzzy/tube distortion sound. As always thanks in advance!