Which Bias Pot is better?

[kramerxxx]

Which potentiameter is better?
The first one has less turns/adjustment and is $1.60.
The second has more turns/adjustment but is $14

Is the second one 9x better?

 

[94Tremoverb]

The second one *is* better, but the first is perfectly adequate for the job.

 

[kramerxxx]

The second one *is* better, but the first is perfectly adequate for the job.

Thanks for the reply. I also posted on the 'Rectifier add bias pot' sticky and was told about the same thing.

This is where I found the multi-turn model.
http://www.mouser.com/Passive-Components/_/N-5g73?Keyword=50K+Multi-turn+potentiometer+Bourns&FS=True

They have cheaper ones so I'm going to order a few of those and give this a try.

 

[fluff191]

The second one *is* better, but the first is perfectly adequate for the job.

+1

I used the Bourns pot on my Recto.

 

[kramerxxx]

The second one *is* better, but the first is perfectly adequate for the job.

+1

I used the Bourns pot on my Recto.

What was the price of the Bourns pot you used? Did you notice a big difference in the overall tone of the amp? And if so, can you describe the differences?

thanks,

 

[fluff191]

I honestly don't remember what I paid for the pot, but I know it was right around $10 off eBay. But I think it was a pack of 3 or something like that.

And yeah the amp warms up a little and sounds a bit fuller, but the trade off is low volume levels (bedroom levels) don't sound great, so if you play a real low levels, keep that in mind.

It wasn't available when I did my mod, but if I had to do it again, I would just spend the money and buy the Bias Mod Kit from Mansfeild Guitars. It keeps everything nice and neat and keeps the capacitor in the circuit incase the pot fails.

http://www.mansfieldguitars.com/order.html

 

[kramerxxx]

Yeah, I saw that one too.

thanks, I don't typically play quite with this amp, afterall, it is a Rec, right.

 

[94Tremoverb]

I forgot to say - if you don't use the Slave output jack, there's a far better way of doing this that doesn't require either of those pots - turn the Slave level pot into a bias control... then you can get at it from the outside of the amp. I also added bias sensing resistors and connected them to the Slave jack itself, so by plugging a meter with a 1/4" plug on the cable in there, I can get a direct bias reading.

The Slave pot is 10K, so if you use it and a 12K resistor in series to replace the original 22K ground resistor in the bias circuit, you get the stock value when it's full up and hotter as you turn it down - but not *too* hot (apart from in Bold/Diode), and it's also fail-safe since like all bias control methods that use the ground resistor, if the pot goes bad the bias voltage goes up, not to zero, which is always the right way to do it.

 

[fluff191]

I forgot to say - if you don't use the Slave output jack, there's a far better way of doing this that doesn't require either of those pots - turn the Slave level pot into a bias control... then you can get at it from the outside of the amp. I also added bias sensing resistors and connected them to the Slave jack itself, so by plugging a meter with a 1/4" plug on the cable in there, I can get a direct bias reading.

The Slave pot is 10K, so if you use it and a 12K resistor in series to replace the original 22K ground resistor in the bias circuit, you get the stock value when it's full up and hotter as you turn it down - but not *too* hot (apart from in Bold/Diode), and it's also fail-safe since like all bias control methods that use the ground resistor, if the pot goes bad the bias voltage goes up, not to zero, which is always the right way to do it.

:shock: :shock: :shock: :shock:

**** that is a good idea. With the Bias voltage going to the jack, you would totally need to turn the amp off then plug in the dummy jack and then turn the amp back on right? Otherwise you risk shorting something? Just curious.

 

[twothemax]

i pmd you. i have a brand new bias kit for the rectifier amp line. very nice and tidy. this unit can be mounted inside or outside your amp chassis. pot, resistor are on one circuit board. complete with instructions.
send me your email and i can send you some pics.

 

[94Tremoverb]

**** that is a good idea.

Thank you, I was quite proud of it .

With the Bias voltage going to the jack, you would totally need to turn the amp off then plug in the dummy jack and then turn the amp back on right? Otherwise you risk shorting something? Just curious.

No - what you do is fit either a 1-ohm 1% resistor to each tube base the standard way (what I did, since I have plenty of them) then parallel the tube cathode ends, giving an effective .25 ohms in total, or - if you can find a 1% one, you could use a single .25-ohm resistor - so you get the average reading from all four tubes, and then connect that to the jack tip contact. The worst that happens if the plug shorts the two contacts as it goes in, is that it momentarily reverts to the stock situation where the cathodes are grounded anyway, so no harm can occur.

You do of course have to remove the original feed from the 4-ohm jack to the Slave pot, that would really cause trouble!

 

[Thatguy]

What are you guys setting your bias to? Right now I have mine at -49v on a rectoverb. Is that still too cold? I don't want to burn anything up.