5150 II/6505+ bias mod/low gain valves worth it ?

[Tawlks]

So, you guys on RT have given me GAS to have my 5150 II bias mod, how significant is the difference, what is the difference?

Also, how much would it cost to get done, not by FJA but by the tech I see, he's pretty good and well experienced, he builds guitars and other equipment for bands so I'm sure he'd be up to it.

Anyone got instructions?

I was also wondering, seeing as I play metal but don't exactly dime the gain, would it be worth changing the V1, or all the preamp valves to 5751s or 12aU7s? Same questions, worth it? What's the benefit/drawback?

 

[skoora]

It sounds like it's just putting a variable resistance bias pot in place of a fixed bias resistor. Any tech can do it with a schematic. Preamp tubes are cheap, buy a few, put 'em in and see what you think. Lower gain tubes will lower the drive but also might lose top end sheen/spank.

 

[Erock]

Eurotubes has a little blurb on their site about the 5150II/6505+ bias mod:

Peavey 5150 II and 6505+

The 5150 II and 6505+ are the same amps and fall into the love it or hate it category. I get calls and emails all the time from players who sold or traded their original 5150's off for the 5150 II or 6505+ and the question is always, "how do I get my 5150 II or 6505+ to have the balls my 5150 had?" Unfortunately the answer is you can't get there from here... The voicing on these amps is totally different than the original 5150 and Peavey choose to basically neuter the 5150 II. It simply does not have the low end grunt and raw sound that the original had. This is not bad, its just different and you will find plenty of players who love the 5150 II.

I'm questioned a lot as to the bias adjustment on the 5150 II and 6505+. This amp does have an adjustable bias but the available sweep is pretty narrow and the only way to get the power tubes out of crossover distortion is to lower the resistance to the circuit and once again this is a very easy mod and well worth it.

Inside the amp there is a small circuit board that has the bias trim pot mounted on it and the final bias resister which is a 12K 1/4 watt resister. All that's necessary is to replace that resister with a 6.8K 1/4 watt resister which will increase the window of available bias adjustment. A final bias setting of between 36 to 40mA of plate current per tube measured with a bias probe is a good setting. You only need to probe one tube, set the bias for it and you’re done.

The bias pot is located right next to the power tubes so if you use a short bias probe you don’t even have to remove the amp from the chassis. We have our own Eurotubes bias probes which can be used with any multimeter that will do this for 25.00

 

[Tawlks]

Eurotubes has a little blurb on their site about the 5150II/6505+ bias mod:

Peavey 5150 II and 6505+

The 5150 II and 6505+ are the same amps and fall into the love it or hate it category. I get calls and emails all the time from players who sold or traded their original 5150's off for the 5150 II or 6505+ and the question is always, "how do I get my 5150 II or 6505+ to have the balls my 5150 had?" Unfortunately the answer is you can't get there from here... The voicing on these amps is totally different than the original 5150 and Peavey choose to basically neuter the 5150 II. It simply does not have the low end grunt and raw sound that the original had. This is not bad, its just different and you will find plenty of players who love the 5150 II.

I'm questioned a lot as to the bias adjustment on the 5150 II and 6505+. This amp does have an adjustable bias but the available sweep is pretty narrow and the only way to get the power tubes out of crossover distortion is to lower the resistance to the circuit and once again this is a very easy mod and well worth it.

Inside the amp there is a small circuit board that has the bias trim pot mounted on it and the final bias resister which is a 12K 1/4 watt resister. All that's necessary is to replace that resister with a 6.8K 1/4 watt resister which will increase the window of available bias adjustment. A final bias setting of between 36 to 40mA of plate current per tube measured with a bias probe is a good setting. You only need to probe one tube, set the bias for it and you’re done.

The bias pot is located right next to the power tubes so if you use a short bias probe you don’t even have to remove the amp from the chassis. We have our own Eurotubes bias probes which can be used with any multimeter that will do this for 25.00

Ahh thanks man. That was quite useful. I'm more concerned abotu the differences between bias modded and non bias modded tone wise, sounds like my tech could do it no problem.