The Amp Garage

PROBLEM SOLVED!!! The phase inverter had a very loose tab on the tube socket! I had noticed when I was chopsticking around, every now in then if I bent one of the output wires on the phase Inverter the oscillations would subside ONLY if I kept bending the wire pretty far... however relieving pressur...

Everything from v2 on is just a straight up superlead; only difference being a switchable cathode bypass cap over the 820ohm cathode resistor and the now changed presence circuit (more like the jcm800). When I'm disconnecting the ground on the presence pot, I'm also disconnecting the 4.7k resistor a...

bepone wrote: ↑Sat Jan 06, 2024 9:05 am something is wrongly connected, or component faulty, t is is simple amp, need to reckeck all from zero

If I was a sane person, I'd do just that . Unfortunately for me, half of the fun in tinkering is the chase!

You didn't mention which impedance tap you used to obtain the feedback. 27K seems too low unless you have a 2 Ohm tap. If you have a two trace scope, compare the phase of the input signal at the PI to the phase at the secondary of the output transformer. They should be in-phase. It's off of the 8oh...

UPDATE: The LARGEST issue has no been mostly solved: my shieled input wires for v1b and v1a had initially been grounded at the filter cap grounds... moving the shield ground to the input jacks has completely eliminated most of the strange oscillations and odd interactions between the tone controls a...

So the mystery deepens! I tried swapping the ot leads and immediately the amp began to howl! So it isn't that... Then after futsing around a bit, I started to notice that if the tone knobs were rolled off to zero, if the presence knob isn't at full, a ground loop buzz became very audible. At other v...

To answer some questions: I'm pretty sure the MV is wired correctly as it functions as expected and there are no squeals or obvious audible oscillations. Same goes for the presence knob, but who knows I could just somehow have the world's most stable amp with a PFB loop haha! I'll be at work for the...

Hello everyone! My main "futs around" toy based off a plexi/friedman idea is giving me a rather strange issue/unexpected interaction. I recently started messing around with a NFB control using a 250k pot acting as a variable resistor and a 27k resistor in series with it. Turning the knob down to its...

Wow, that's exactly the kind of result I'm looking for. So that youtube video, did that have the extra valve? Or is that video of just the Express preamp (kind of like I'm doing) but with some tweaks? (like Mark A's suggestions?) Mark Actually - if you had a schematic to share that would be great. ...

I did the exact same thing you did here with my own little build; I got gobs of gain offa it. I did however, add an additional preamp valve in order to simulate PI gain and add a cathode follower for a better output impedance match. https://www.youtube.com/watch?v=IDGd4GfbqtM It's since been convert...

i'm probably not doing the "correct" thing here, but I've been using a few relatively non-colored hifi receivers with some flat speakers to mix different things/ playback guitar. The flatter your whole system, the better. My main setup has been an older 70s realistic unit that is relatively color-le...

Been messing around a bit more and swiped the last two stages of the Bogner Fish in order to try to implement presencr how it was done in in that circuit; and I must say its much more effective than I expected. The only oddity I've noticed is that when the presence is maxed, it seems more like a mid...

Thank you both for the reply. One other question- For builders who make tube preamps/tube pedals- is it typically just taking the amp schematic and then recreating that or are there other things that would be changed? You can very well just chop the preamp section from before the PI out of a generi...

I know this thread is a bit older.. what does "filtering" when it comes to building a preamp or other tube pedal refer to? Filter capacitors. IE the big caps that get rid of the ripple/switching noise from the power supply. Typically encompasses if you're using a choke/include the stepdown resistor...

https://youtu.be/vk9b6LPfFOs By no means is this a DLM, but it is a higher gain circuit with a single ended output stage that can really push some volume. Also it does more than just the 68 specs, lol. Single ended 6550s in parallel in this video. Huge OT. Biggish PT. N Choke. I've since put some e...