The Amp Garage

I had built an amp that was working fine until I flipped the power on and off rather suddenly and the HT fuse blew. But so did one of the rectifier diodes. Took me a while to find the bad diode since it still read 200 ohms- in both directions. But that makes sense as the bias circuit I used was just...

I'll make some more tests this weekend. I will say I was monitoring the HV secondary and it began to come up with the Variac then the fuse blew out at 231 volts DC. After that it wouldn't even do that any longer. Nothing. The filament was flat dead. As I recall I measured the filament taps and they ...

I've completed an amp build and it's worked fine up to the other day. I turned the amp on and upon hearing the buzz of an unconnected input cable, shut it off, quickly plugged the cable in and then turned it right back on. It blew the fuse. I should add the amp is plugged into a Variac that was cran...

Why does it have to be a "Power Mosfet" as opposed to a signal level Mosfet?

silverfox.

So then it sounds like the wrong grid resistor could cause distortion and/or red plating depending upon which way the error goes. Too high a value, overheating, too low, distortion?

silverfox.

What these questions relate to is the changing of output tubes from KT88 to 6L6. I'm trying to determine if I need to change the grid stoppers to somehow match the 6L6 output tubes. Another question- If there is no substantial current flowing in the bias circuit, how do different value bias feed res...

How does one determine what value grid resistor should be used on the output tubes? For example 6L6 vs. KT88? Is it the plate voltage or the tube characteristic?

silverfox.

I finally bought the trannies a couple weeks ago and received them from Amp Parts Direct in FL. Great service. They are 6.6K and as far as I know I'll be running them at 450 VDC B+. The output tubes are likely going to be JJ 6L6. Seems like 450 V is high but I've seen them run at much higher in the ...

I'm putting together a stereo power amp for guitar. I think I finally got all the bugs worked out with the 6L6 version of that Sunn 100s amp. My intentions are to run two of the Classic Tone 30 watt TW OT and use the PT from a Carvin MTS 3200 100 Watt amp. I had forgotten the 6L6 biased correctly wi...

Yes I realize the PT will be sufficient and the one I have on hand is from a Carvin 100 watt, MTS 3200. I want to make sure Classic Tone is a good buy and the 6.6k is a good match for the 450 B+. There also will be two on the chassis as this is a stereo power amp; so 60 watts total. I'll delve into ...

As I recall Classic Tone has a good reputation. I'm in the process of putting together a stereo power amp based on the Sunn 100s output section, but using 6L6's running at B+ 450. The OT's won't be UL. I was looking at the Classic Tone Trainwreck OT with 6.6k primary as output. Is there any reason I...

Thanks JD. I just checked back into this thread. I've been working on getting a power amp debugged and I've gotten that done now. Kinda off in a bit of a tangent but still collecting information on the Super 78.

silverfox.

If you search Meas Boogie schematics you'll find they use current regulating diodes on some of the preamp tubes. I've seen it in the past but couldn't find a good sch. for this post. Another one I've seen is the use of a FET on the cathode.

silverfox.

Tell me more about living in "Factory Town". Makes me wonder if this is in the US as most "Factory Towns" are KaPutt. Maybe the power company needs to check the voltage regulator at the substation...

Is the remaining Hum at a normal level? Perhaps your done.

silverfox.

I wonder if I should buy the 3 vol. set? Is there anything beyond layout information and construction techniques- Yes I realize you quoted the voltage regulation theory. Sometimes a book can be rather anti-climactic. I'm curious to know also what the impact of the regulation would be on any high gai...