r/ToobAmps

Build using el84 tubes

Am I right in thinking that r 28 sets the starting point of the bias pot

if so can I put the centre lug of a 10k bias pot at c- and then one outer lug to r21 and the other to r22 after replacing R28 with a 5k resistor to accommodate for the 10k pot put in the mix

Or is r30 the governing resistor

Trying to ensure I don’t offset the biasing start point too much

Thanks

I'm dumb. Explain how the plate resistor turns this 12AX7 triode from a current amplifier into a voltage amplifier. Explain how the cathode resistor voltage changes with the plate resistor voltage. I read the garden hose analogy on Rob Robinettes page 25 times and cant figure out what the hell he's talking about. I want to understand this in an analogy to a garden hose and water pressure but I also might be able to understand it in terms of voltages and current. I redrew the schematic. Im a little worried that filter cap is not drawn in the right place. EDIT: Please note: the cathode resistor should be connected to ground.

Can someone explain why fender added the 0.01uf capacitors into the mix and can I re instate this arrangement into the Hoffman pro jr circuit

Also any reason Hoffman might have replaced the CR5 1N5062 with a 1N4007

Thanks.

Getting this CHA-20 up and running (finally) and having one slight issue that I'm having trouble figuring out!

Ok so on the schem there is a 2w 68k resistor that ties the 6v6 screens together which leads off to the 50uf bias cap.

In my picture, there isn't one.

What effect would this have on the amp? The amp works, makes sounds etc but is fairly distorted (anything above 1/4 volume is distorted) and does this kind of weird tremolo / sputtery / note decay thing.

Amp has been fully recapped, voltages per the schem across the board are basically spot on with a variac set to 110v.

At some point in its life, one of the 6v6 sockets was replaced and I'm thinking that the amp never quite worked right after that 🤷🏻‍♂️

Anyhoo, just thought I'd ask smarter people than me their thoughts on the matter

How do I get a guitar tone to sound like this

Guy I work with had a friend moving back in Arkansas,, was getting rid of stuff. He had the good sense to save this survivor 1947-1949? Montgomery Ward amp. When he told me, I thought maybe a Teal Stripe Bandit or something. When I saw this... I started to get a bunch of tickets (I'm a chef) but I wanted to see inside. I was not disappointed. Someone had put a three prong plug on it.... But I haven't looked actually inside. Thought you guys would be as tickled as I was. A few of you surely would know more about it than I (which isn't difficult). Yes we know. Just because it's rare doesn't make it valuable lol. Not even trying to sell this just showing you guys.

just snagged this off facebook marketplace for a nice deal! has anyone ever tried this with the Weber DT-10P? Weber claims they come close to the blue alnicos but i’m hesitant to believe that.

I have tested everything I can test with a multimeter and everything looks very close to spec. I re flowed the solder joints and everything that should have good ground connection, does, yet the Reverb signal is still somehow making its way to the output. It’s very faint, but it’s there and it’s bothering the hell out of me.

Could this be a bad pot? It tests ok.. but it doesn’t make sense that the reverb isn’t getting fully grounded.. anybody shed some light on this? Can pots fail in this manner?

Supersonic 60 schematic in photo..

So I've got these 4 amps and a bass head that I'm trying to decide what to do with. They are;

Ampeg V4 Bass head - function unknown, roadside rescue

Kalamazoo Bass 50 - functional but very quiet, roadside rescue

Line 6 Spider II - functional

Marshall Lead 12 - functional

Crate RFX15 - functional

The catch is i don't even play electric guitar, and haven't had a need to amp my acoustic in ~25 years other than to mess around.

I'm considering restoring the Ampeg and Kzoo. I would likely sell it give the Ampeg to a bass player i know. From what I've read the Kzoo is a terrible bass amp but it might sound nice using it for an acoustic guitar. The 2nd pic are the tubes in the Ampeg. If the glass has a mirrored spot does that mean it's shot? It also has a blown fuse so I haven't plugged it in at all.

I know that model of Marshall has regained some love in the community lately. It really just needs a good cleaning

The Line 6 and Crate, I'm not sure. The Crate is the only one I bought myself just for dicking around years ago.

I doubt i would get much in the way of trade in value for the 3 small amps. Kzoo and Ampeg, maybe, maybe not.

Help me make the right decision wise community

well nothing extraordinary has been done here.

any other mods are related to the preamp/phase inverter

1. plate voltage from pin3 to ground is 501.5
2. bias voltage from pin5 to ground is negative 47.9 when standby on and 46.8 when standby off
3. screen voltage from pin4 to ground is 502V

I will take out poweramp pcb to see what is going it, but it already had traces of burn under those 700ohms screen grid resistors. That's why I changed them for 1k

+ I added electrical fan but I just took wires from F1, add additional full wave rectifier to power the fan and it's working so that is not this

Stumbled upon my new favorite amp, a new handwired series Vox AC30. The combination of this amp with my strat is every thing I've been looking for when it comes to edge of breakup and bite with an adaptive feel. I was blown away.

Now, any advice on pedals that pair with Vox nicely? I've heard they're not always the best pedal platforms, any advice is appreciated!

I built this 5E8-A from the Mojotone amp kit and upon firing it up for the first time it’s got this terrible high pitch squeak. It changes some when I turn the treble control, but other eq/volume pots do nothing. I’m also not getting any sound from the input jacks when I plug something in. It’s just squeals.

I’ve checked continuity everywhere on the board near as I can tell. Also checked continuity on the tubes, though I don’t have a tube tester.

Not really sure how to troubleshoot from here. Any help would be greatly appreciated. Thanks!

EDIT: Thanks for the help everyone! Got it working great. It was indeed the output transformer that was wired backwards. I had wired it correctly according to the instructions so either the instructions had the colors wrong or the transformer was made incorrectly.

Hey All! I just picked up this original 1970’s Ampeg Model V-9 for $900. Im new to playing guitar and bass but was curious if I got a good deal…I can’t seem to find any for sale online. Everything works other than the reverb spring is loose and needs to reconnected it sounds like. I only picked it up since it seemed like a good deal but it’s massive and I don’t really need something this big. I can’t seem to find any for sale online marketplace or reverb so insight for reselling would be greatly appreciated since I’m hopefully going to fund my new setup with the money made. Thanks!