Okay, went a bit over my head on that one. First, what exactly does HT stand for? Also, I never mentioned anything about a resistor at all, so I don't think I did say it haha. the two methods I mentioned were to leave the switch in it's stock location but run a flyback diode in parallel with the choke leads or to relocate the switch & run a .22uf cap to ground off the switch. How would I incorporate a resistor into the rewire? Why would I use it instead of a cap/diode?
5150 Mod Thread
- Thread starter Wolfeman
- Start date
TheWinterSnow
Den Mørke Natt
HT = positive supply voltage.
I meant when I said that you basically mentioned the best method was to rewire the switch. The actual location of the switch should be before the rectifier for numerous reasons. Then I added, in order to allow the capacitors to charge up before the standby is switched on so that you prevent the choke from blowing up your amp, you place a resistor in parallel with the switch, high enough so that the amp isn't on, but low enough so that the caps can charge slowly as to not set off the transient spike (or inductance kick) of the choke.
I meant when I said that you basically mentioned the best method was to rewire the switch. The actual location of the switch should be before the rectifier for numerous reasons. Then I added, in order to allow the capacitors to charge up before the standby is switched on so that you prevent the choke from blowing up your amp, you place a resistor in parallel with the switch, high enough so that the amp isn't on, but low enough so that the caps can charge slowly as to not set off the transient spike (or inductance kick) of the choke.
So would you recommend using the resistor in place of, or in addition to the cap snubber to ground off the switch?
TheWinterSnow
Den Mørke Natt
Just the resistor, in place of the diode, no cap. The only downside of it is (although it is the best design for the life of your amp) that you get a small amount of signal coming out of your speakers with the standby on, although if you wanted the standby as a mute function if its really that important, add a kill switch to the input jack of the amp.
Here is an article on the topic with pictures:
http://www.freewebs.com/valvewizard1/standby.html
Here is an article on the topic with pictures:
http://www.freewebs.com/valvewizard1/standby.html
Gotcha. So, given your in-depth knowledge of these amps, could you possibly recommend an exact resistor spec to put in parallel with the switch?
JakeAC5253
Frozen Sun Audio
- Nov 19, 2010
- 936
- 1
- 18
I recently played with a 5150 mod to fill out the sound while keeping the original voicing and feel. It was supposed to be a single component mod that turned into a dual component mod just to balance it out. Funny story to it actually. I was having a look at the schematic for the original 5150 and I noticed one component value which made no sense to me. I thought it was a typo before I opened my amp and found that it was indeed correct. I started by wiring a 1M pot in series with R101 in order to use it as a feel knob to change the way the amp felt. A friend and I both thought that all the way up sounded like junk compared to the rest of the sweep, and I said ahh that's alright, that's the full up mod value, can't expect it to all sound good. After I disconnected the pot I realized that I had wired it backwards and full up was the "stock" amp value with the pot resistance set on 0Ω and the amp's stock resistor only!
The mod was born, but it needed tweaking. I raised the value of R101, values between 220k and 470k work, but any higher and the amp can tend to feedback pretty bad, noise gates still work, and so do the knobs on the front. I lowered the R9 value to somewhat balance this out, but I didn't go nearly as low as the suggested Cameron mods. 250k, 330k, 470k, 680k are good values for replacement for R9, any lower than a single 250k resistor there and you absolutely decimate the amps voicing and feel. This goes for impedances created by more than one resistor as well (the original mod said to put two resistors in parallel). If you did this, beware that you are creating an impedance value that may well be much lower than you think it is (applies to noob modders only) and I would recommend playing with values much higher than what Cameron suggested.
Reading the entire thread somebody mentioned that they did the power tube bias mod and still had fizz... TRY THE R101 MOD NOW!!! ...no more fizz whatsoever.
The mod was born, but it needed tweaking. I raised the value of R101, values between 220k and 470k work, but any higher and the amp can tend to feedback pretty bad, noise gates still work, and so do the knobs on the front. I lowered the R9 value to somewhat balance this out, but I didn't go nearly as low as the suggested Cameron mods. 250k, 330k, 470k, 680k are good values for replacement for R9, any lower than a single 250k resistor there and you absolutely decimate the amps voicing and feel. This goes for impedances created by more than one resistor as well (the original mod said to put two resistors in parallel). If you did this, beware that you are creating an impedance value that may well be much lower than you think it is (applies to noob modders only) and I would recommend playing with values much higher than what Cameron suggested.
Reading the entire thread somebody mentioned that they did the power tube bias mod and still had fizz... TRY THE R101 MOD NOW!!! ...no more fizz whatsoever.
JakeAC5253
Frozen Sun Audio
- Nov 19, 2010
- 936
- 1
- 18
I made an audio demo of my previously posted mod. And here are the clips:
Preamble (details about mod and setup): http://dl.dropbox.com/u/8838613/5150 Mod Audio Demo/5150 Mod Demo Preamble.mp3
Crunch Channel Demo: http://dl.dropbox.com/u/8838613/5150 Mod Audio Demo/5150 Mod Demo Crunch.mp3
Lead Channel Demo: http://dl.dropbox.com/u/8838613/5150 Mod Audio Demo/5150 Mod Demo Lead.mp3
The clips are long but detailed. Hopefully I've shown the tone effectively, like I said it's not so much better as it is different but also useful, which is why I wired it up to a switch so I have both tones at my disposal.
Preamble (details about mod and setup): http://dl.dropbox.com/u/8838613/5150 Mod Audio Demo/5150 Mod Demo Preamble.mp3
Crunch Channel Demo: http://dl.dropbox.com/u/8838613/5150 Mod Audio Demo/5150 Mod Demo Crunch.mp3
Lead Channel Demo: http://dl.dropbox.com/u/8838613/5150 Mod Audio Demo/5150 Mod Demo Lead.mp3
The clips are long but detailed. Hopefully I've shown the tone effectively, like I said it's not so much better as it is different but also useful, which is why I wired it up to a switch so I have both tones at my disposal.
Hello. Forgive me for reviving an older thread but ... does anyone have suggestions for taming the HISS in the Peavey 5150 (2x12 Combo)?
I've been in touch with a few technicians who suggested replacing most of the plate Resistors in the preamp with 1% Metal Film 5w of equivalent values. If anyone has done a "hiss reduction mod", can you post which changes, in detail, you made had the most effect? (I'd be working on the combo, so component numbers might be unrelated/irrelevant between head schematic and combo schematic).
Thanks in advance for any advice anyone might have.
I've been in touch with a few technicians who suggested replacing most of the plate Resistors in the preamp with 1% Metal Film 5w of equivalent values. If anyone has done a "hiss reduction mod", can you post which changes, in detail, you made had the most effect? (I'd be working on the combo, so component numbers might be unrelated/irrelevant between head schematic and combo schematic).
Thanks in advance for any advice anyone might have.
I’m trying to figure out this mid sweep mod I’m not good with diagrams and the only pcb layout I can find is for the 60 watt combo.if I could find the 120 watt pcb layout I think I would help unless someone had a few pics of where the mid sweep mod would go .i can’t seem to find the slope resistor or r28 if I’m even in the ball park.anyway it would be cool to sort this out maybe with some help I could .thanks!
