The Amp Garage

The previous owner of the Quad had the grill cloth and baffle rebuilt. The Twin is on loan from a friend .

I don’t get to play these too often, but the Super Six is going to get some exercise this weekend at a backyard party gig.

I just got my amp’s brother, a Quad Reverb. And what I mean by brother is that all the transformers, save the chokes, have the exact same date codes between the amps. They must have been on the assembly line at almost the same time. IMG_7543.jpeg IMG_7556.jpeg That twin reverb looks like a small amp...

Where did you get these from? So someone else doesn’t get these.

…or, possibly also taking some high frequency negative feedback from the IT output/6v6 input via a cap and resistor ala mid 70s silverface twin. Looks like I’ll need to get familiar with my scope again if I’m going to play around with this, haven’t used it in a decade.

Yes, there’s a potential that a feedback loop around both an interstage and output transformer might shift from being negative at lower frequencies towards being positive at higher end of the frequency range. So looking at the schematic for the MM, a place to inject the feedback could be at the V1B...

Did you ever get around to making this?

I’m planning on a Musicmaster influenced build with some differences. Was wondering about attempting global NFB, but the phase shift of the interstage transformer is a problem with that, right?

I saw this today: How To Use 5V Tap to Convert from 115V Primary to 120V Primary (Mark Fowler) http://www.ws.binghamton.edu/fowler/How%20To%20Use%205V%20Tap%20to%20Convert%20from%20115V%20Primary%20to%20120V%20Primary.pdf Any potential negatives to doing this? Sorry if this has been discussed before...

Hah, when everything is buttoned in the cabinet and the trem clicked on, I can hear the ticking at a very low level (intensity “1”). It’s low enough that I’m not really bothered by it, and I would mostly use the foot switch anyway, so it would only really be an issue when the term is switched on and...

No discernible ticking in the amp with the intensity all the way off. One sort of mod I did was solder in a solid lead from the aux speaker out ground where the OT is connected to the normal speaker out ground. In my mind it is not good practice to count on the jack grounds to connect through the ch...

I only played it for a couple of minutes to make sure it worked. I didn’t scrutinize it enough.

I assume this ticking would be when the circuit is “on”, but intensity is”1”?

Removed out the old roach and instead the new one. Tremolo works good now.

Ordered a roach from Antique.

Besides possibly playing with the NFB values from the speaker, is there anything to be had by altering the other feedback circuit (220k/.01uf from the PI output)?

In the dark didn’t change anything, nor did swapping in a different good 12ax7 into v5. With the roach disconnected from the pot, it read about 3M. With the light flashing, the lowest reading I got on the meter was 280K. Again hard to say with oscillating readings, but I would think that lighted res...

Roach LDR reads 20ohms at 1 intensity, and between 37-43K at intensity =10. I’m sure my multimeter is limited in reading the oscillating values, it’s a cheapie Radio shack one.

Well, the roach does light up when shorting the Jack directly. But the vibro shunting affect is weak. Here’s the v-5 voltages: (Vibro “off”) 1: 429V 2: -36V 3: 0v 6: 380V 7:-36V 8: 5.8mV Vibro “on”, intensity and speed at “1” (shorting jack input to ground, roach pulsating ~2.5x/second): 1: 130-390V...