Well, phase one of the Renegade 410 restoration is complete!
I first turned-on the amp without output tubes (or schematics) and the amp didn't turn on! Let me re-phrase that... there were no pilot lights illuminated on the front panel. The PT was humming a little bit and I saw the filaments lighting up in the preamp tubes so I knew
SOMETHING was getting power! I pulled out my Fluke 73 meter & trusty wooden chopstick probe and start poking around and found 2 problems.
First, a quick disconnect connector was stressed to the point that it broke inside the clear tubing so it held together but the pressure placed on it from the wire bundle being too tight (with no service loop) had pulled the wire free from the connector and no continuity was the result. I removed the broken Fast-On connector, replaced it & pulled a little more length through the wire bundle to prevent an encore.
Next, I found that one of the plastic fuse holders on the far left (viewing from the front panel) had a broken pin and only one side was actually soldered into the circuit board. Since the pin broke, I removed the fuse holder from the board, soldered some wire leads to the contacts, insulated it with heatshrink tubing, soldered the wires to the PCB pads and affixed the holder to the chassis with a piece of VHB double-backed foam tape.
The amp now turned on, the footswitch worked and all the tube voltages looked good.
I installed a pair of NOS Tesla EL34LS output tubes (on the EL34 side) and a new pair of Electro-Harmonix 6CA7EH (on the 6L6 side), biased them up according to the recommendations in the manual (but the 6CA7s were biased a bit colder than the EL34s for little higher headroom). I then confirmed output power and smooth noise-free operation of all controls and functions (all the while with the amp connected to a bench load and the output monitored on an analog oscilloscope).
While I was "under the hood", I elected to install an NOS JAN Philips 12AX7WA (long plate) in V1 (Clean channel), a selected (low microphonics) JJ ECC83S in V3 (Gain Channel) and a selected (balanced halves) JJ ECC83S in V6 (Phase Inverter). These tubes had no apparent noise problems (i.e. shot noise or sizzling) or microphonics and were very quiet. The JJs were pre-tested and selected by Bob Pletka at Eurotubes.
I reassembled the amp and did a static burn-in for 3-hours while occasionally checking for microphonics, control noise and anything else I could learn about the amp without actually playing through it. It was late and I didn't want to wake the wife! The only potential problem I noted was when Channel 2 had its Gain & Volume controls turned up past about 2 o'clock the amp squeals (with no input). The squeal can be "adjusted" with the Treble control, bright switch and Presence control as I expected. I need to look into this with a guitar connected but I expect that there may be a tad too much gain (or a problem with wire-dress) in this channel as it is currently tubed-up.
I really like the serviceability and layout of the amp. Despite some overly-tight wire harnessing and lack of attention to the minor details (like heatsinks and regulator tabs too close to electrolytic caps and caps/resistors sometimes bent dangerously close to adjacent pads and components), the amp seems to be well built and layed-out. I LOVE the chassis mounting method with 4 large "hidden" bolts. I wish everyone would mount their chassis in a similar fashion!
Tomorrow I plug in a guitar and see what it SOUNDS like! That will be the big payoff for my day of amp rebuilding and repair (I also dug into a non-functioning Marshall Haze 40 but will have to get some parts before I can finish it up, even though it does now work).
Steve
http://www.eb100s.com
http://www.musicmanamps.com