The Amp Garage

Since you have already blown one fuse, I'd save yourself the cost of additional fuses (and other more expensive parts) by building a lightbulb current limiter. There are instructions on this forum as well as elsewhere on the net on how to do this.

Mike

At 400V with a 220k plate resistor, the range is about 0.1mA to 1.5mA. The oscillation goes from about -4.5Vgk to 0Vgk regardless of the DC bias point. LFO 220k 400V.png At 400V with a 470k plate resistor, the range is about 0.1mA to 0.78mA. LFO 470k 400V.png Oh! The load line makes alot of sense. ...

So, I tested my remaining 9 opto-couplers all at 1ma and they were all pretty consistently near 540 ohms. That is pretty much spot on for what I measured for the part I made the curve for. So, I did not test them any further. They are pretty consistant. So, I don't think they are rejects from a line...

Given that the optocoupler coating seems to be translucent (FFS! :roll: ), did you take those readings with the optocoupler wrapped in something opaque, eg black insulation tape? Yes. The part was inserted into some heat shrink tubing. Then each end of the tube was clamped with a forceps with a len...

My bag on repro vtl5c1s appeared today. So, I started to test one out. Right out of the gate, I discovered that the plastic case is *NOT* light proof. With no connection at all to the LED I could get wildly differing resistances just by waving my hand around near the device. And the max resistance (...

Thank you so much for posting these numbers. They will help alot in knowing what I'm looking for the part to do. My guess is that I'll not luck out and have useable chinese vtl5c1. I may have to search for an alternate opto-coupler to use that is still in production. Maybe something like a nsl-32 wo...

A guy on another forum had trouble with some of those that he had ordered on Amazon. I ordered in some, waited a few days and ordered some more in order to possibly have two batches. After testing them, none of them were anywhere near a VTL5C1 and were useless for the trem-o-lator. Maybe you will h...

I highly recommend not to do the mod in stages like you plan. It's a fairly simple and straightforward mod that's easy to undo if you get hung up. I hope you found a stash of Vactec/Vactrol optos. A few people have had issues with the Xvive optos. I'll be following along with interest. This should ...

You're not going to want that SPST switch above the 50kRA pot. It will make the Vibrato channel louder when open. If you want a switch, you can put it across the foot switch jack or in the path of the LED. I've already got the switch on the amp. And it does do exactly what you say. It reduces the l...

I've just ordered a bag of vtl5c1s and am getting ready to convert my stunflower over to a Trem-O-Nator. Where did you order those from (please don't say Amazon). Umm.... Well... I won't say it then but that is where they were ordere from. They did say they were vactrols. BUt I'd not be surprised i...

Change the cathode resistor to 10k or larger, like 47k. The 2k7 cathode resistor will steal current from the LED. There is a large amount of variation amongst VTL5C1's. Some work fine with a 470k plate resistor and some need the extra current that a 220k plate resistor provides. I seriously doubt t...

I've just ordered a bag of vtl5c1s and am getting ready to convert my stunflower over to a Trem-O-Nator. When it is possible, I like to do a bit at a time and test as I go. So, I'm thinking of doing the conversion in two steps. The first would be to replace the driver stage and bug with the vtl5c1 (...

So, I installed a 270k/820k voltage divider in place of the 1m grid leak on the reverb driver tube. And it did totally and completely clean up the messy signal that was being injected into the audio channels. However this (unsurprisingly) did have an effect on the reverb itself. The reverb knob was ...

Is it a "bandmaster reverb"? If so, I have a theory on what you are hearing.

Mike

So, much for the grid stopper idea. I tried various values from 39k to 100k and they made no difference at all. I'm starting to think that I may have stumbled onto the "blackface sound". This distortion is there on all channels from about 5 on the dial on up. And it is there all the time. Even when ...