Tube Amp Archive

Wow! Didn't expect that to pop up!
And with the other tan suede ODS Reverb too!

I'd be interested to hear what serial number it is. Did they mention if it is running off of 6L6GCs or EL34s?

Looks great! Are you liking the way it plays? -Dan Thanks, Dan! Here are my observations after about two weeks of playing it. I don't have any single coil guitar right now, just two Gibson Explorers with AlNiCo humbucking pickups, so it may be overdriving a lot earlier than you would with a Strat o...

Thank you, Martin! I appreciate the kind words and all your helpful advice! (I love how that updated bias circuit works). I didn't get any pics, but I did put the FET back in for a bit, on its own with the special input jack like on the originals. It was ok, but I wasn't really that impressed with i...

Finally had the time to finish it up last week. Been putting it through it's paces, testing out different settings and breaking it in. Removed the FET Board and Relay, left it just with the OD footswitch like the original was. Took the 50K OD Trimmer off the board and added a control along the back....

Interesting! Fascinating to see how the output of V2 is set up. There doesn't seem to be a 180k resistor to ground from the 1M/10nf junction and I'm curious what the value is of that mica cap bypassing that 1M? 🤔 Maybe it was modded by HAD or Kitty Hawk at a later date where they added in the PI bal...

I'm really enjoying tweaking the OD entrance trimmer and playing around with different settings. I have notice that the Accent switch doesn't have as much impact as I thought it would versus a full presence control. Should I try a 2.2uf cap instead and does it have to be an electolytic or could I us...

Update: I got the FET up and working. It sounded ok, but nothing that really jumped out to me. I preferred the amp on its own. I may look at a separate FET pedal in the future. Otherwise, the amp is fantastic! I've removed the FET board and switching components and converting it to a single footswit...

Got this on my reverb feed this morning, ODS #112. https://reverb.com/item/91226891-1990-s-dumble-overdrive-special-50-w-head-sn-0112?utm_campaign=Feed-Email&utm_content=feed_listings&utm_medium=email&utm_source=braze&utm_term=Feed+Email gl3oe6nihrwan44okoik.jpg qdvwqgwyvpfflvl6vgux.jpg Seller says ...

My apologies Martin, I mistyped! I should be that I got 8.75 VDC at the bottom of the 10K pot and 3.44 VDC at the top. So, a ~2.54x difference with 4k measured at that point on the pot. I'm going to try the 3.9k, wire everything up, and see how it goes. Thanks again for all your assistance, Martin! ...

Update:
I did find some 3.9k resistors I could use instead.
Matt J.

Yes, it will move when you switch to B+ power. I would connect it to B+ and bias with that. Connected the B+ up and tested the voltages. The closest I got the 2.5x ratio was ~8.75 VDC on the bottom and ~8.45 VDC on the top with the pot measuring ~4K resistance. I do not have a 4K resistor in stock ...

Attempted the biasing method again with two 9V batteries wired for 18V on the new PCB board. I get ~18.23 VDC at the base. Adjusting a 10k pot instead of a fixed resistor gets me to the 2.5x voltage of about 7.292 VDC when the pot is at 5.6k. I do not have a 5.6K pot at the moment, but do have some ...

The FET is 2N3823 from Mouser if that makes any difference with biasing.
Matt J.

You want to get the voltage at the drain to be 1/3-1/2 of the voltage at the top of the drain resistor. 1/2 is ~center biased, 1/3 will give you a bit more FET distortion. It seems like that's where HAD liked it based on measurements posted by CW and shown in traced schematics (i.e. SSS 002). Runni...