Biasing a RH50T / RG50TC

Hi there,

i own a Randall RH50T with two EL34 output tubes.
How to bias it?
There is no randall service center where I live, so I have to bring my amp to an other technician.
How to use the bias plug and the two white trimpots on the back of the RH50T?
A reply here was very kind.

Thanks and best regards
burny

Wow, great response here.


I e-mailed Randall USA because of the question how to bias an EL34 Randall RH50t/RG50TC.
I got a reply, but it was useless. No information, just the hint "almost like Marshall". Without the info which Marshall and so on.
Useless.

I also e-mailed the european Randall distributer. He forwarded my mail to technician that works for Randall Europe and he replied me in my language (german). Here I post a translation:

" on the back there are two trim pots and three measuring points. Each trim poti controlls the bias amperage per tube (exactly the bias voltage and by that the amperage). The three measuring points: one is mass, two are the fall of voltage per tube via a measureing resistor.
So, switch on the amp, standby on, no signal, speaker attached. Measure the voltage (DC Millivolts) from mass to the tubes measuring point.
Adjust the values identically to each tube via the trim potis.
32 to 45 mV are o.k..
Higher values are critical, lower values make the amp sound muddy/squishy."

That's it. Maybe that might help the one or other RH50T/RG50TC-player. Non-tecchies maybe better bring the amp to a randall or other technician and give him this manual.

See you
B.

:roll:
Well they dont seem to be that interested in answering questions and keeping their customers happy.
Ive tried several times to get the answer to this biasing issue, as Randall designed it with the trim pots its a wonder why they want this to be a secret.
Ive set mine on 40 mV but im not satisfied I think I might have a problem in the preamp stage.
By the way It would be interesting to hear from other owner how does your clean channel sound? Mine is extremly weak and sound really shitty. (all Tubes have been renewed).
I bought mine second-hand purely on good reviews in both English and in a Swedish magazine and I did not try it properly before purchasing. (I WONT GET FOOLED AGAIN).

P.s. Thera are other companies that have a differant approach to their customers. I own a Tech 21 Trademark 60 and the footwitch stopped functioning properly. I sent an E-mail to the company and the day after I got an email answer that they had sent a new one that i could pick up at my local Guitar shop. No big thing you say? I live in Sweden and Tech21 is in USA. a week later the shop in sweden E-mail me and say I can come and pick it up, no charge!!!

Lars Jansson said:

....
By the way It would be interesting to hear from other owner how does your clean channel sound? ....

Click to expand...

Mine sounds o.k. on the clean chanel.
Not as good as better Fenders or so, but still fine, better than my Engl.
Without boost it stays clean until gain at around 12 o'clock.
I set my clean gain to about 14 o'clock. With hitting the strings soft it stays clean, with clean boost and hitting strings hard it has a nice crunch tone.

What is your problem with the clean sound?

Btw: i think the main strength of the RH50T/RG50TC are the drive sounds, not the clean ones.

Hi guys, I just checked this thread for the first time to see if there was any info on biasing an RG50T (I'm mainly an MTS fan) and I found your discussion interesting and useful. So, the reason I was looking is because I wanted to try a set of 6L6's to see if it improved the clean tone. I like the 6L6's better than EL34 in my RM50 and so I thought it might be interesting to try some in the RG50T. Has anyone else tried this? I think the RG50T is a great little versatile amp (especially upgraded with a V30 speaker), but I agree with you guys that the available documentation is quite poor. Dave

Anyone know what Mv values a set of 6L6 would need to be set at?

I've never seen an RG50t but does anyone have any pic of the insides,trim pots Etc.???
6L6 tubes I believe get biased some where around 25 to35 mv per tube.That's the range I use.

Best i could do with out taking the back off

Trim pots on left and right and Three prong connector in the middle.

unearth said:

Best i could do with out taking the back off

Trim pots on left and right and Three prong connector in the middle.

Click to expand...

I would say the one in the middle is ground and the contacts on either side would be for each tube.I would take a multi meter and set to milivolts,and some small alligator clips and connect the black to middle and red to one of the outside pins,and take a reading,if it is 25 to 35 it's per side,keep the red and black isolated from each other.This is what I would do if you feel comfortable.

Yeah Might give this a crack in the near future but I got a pretty good deal on a new matched pair of EH EL34 valves so I'll be keeping the EL34s for now.

Thanks for the help