Randall RD45 sloppy chugga clip

Hell Yeah. I think it sounds great. Btw, did you do some preamp tube swaps? Or are the ones you described stock? I'm really getting close to pulling the trigger on one of these.
 
Thanks. The recording sounds a little blanketed. The amp is not as in your face as many others are. You really have to turn some knobs to get it out of the flat feel that it has IMO. I haven't tried an equal in the loop yet. Soon though. I also do like this one more than the 100 watt version. The 1 watt version is fun but don't expect much volume from it of course. It's perfect for playing around my 2 year old because if he hits the volume knob it won't deafen him. It has its purpose.

The stock tubes are all Ruby... 6L6GCMSTR for power and 12AX7AC5 HG for the pre. So yes, I replaced 2 of the preamp tubes and biased the amp.
 
Thanks, that sounds a lot like my RD20H but maybe with a little more body. What speaker are you running it through?

Can you post or PM me a run-down of how to bias this amp? I'm having trouble finding the information & could really use it.
 
I was running it through an Avatar Contemporary 2x12 with Mesa/Celestion V30s in it.

I used a probe to bias it. It's ideal since the trim-pots are on top of the chassis. What is nice is that the amp has a separate trim-pot for each of the 2 tubes. So GJgo, if you were looking for test points in the amp I really have no clue.

My plate voltage was 476mV but keep in mind everyone's is going ot be a bit different although usually in the same range.

Did you still want details on how to do with a probe?
 
Thanks slaveunit, details on how to do it with a probe would be great. I'm looking forward to testing out some Tung-Sols & JJs in there soon. :)
 
i am not opether from GAB sorry.
Saw its rd45 is at 440v too.

Find it is pretty big difference...

Would be great to know the ''standard'' factory plate voltage.

BTW, I asked music corp the max dc bias current the OT can handle, here what they answered : I'm very sorry but those specs are for internal use only and are not available to the public :aww: :thumbsdown:

they just say factory bias is 35 ma, but don't know for what voltage, gonna ask them.
 
GJgo":3p7ftpyj said:
Thanks slaveunit, details on how to do it with a probe would be great. I'm looking forward to testing out some Tung-Sols & JJs in there soon. :)
Click to expand...

This is one way to do it. I actually took my chassis out of the headshell so I don't know if a probe will fit without doing that.


So this will run you $55 plus a few bucks shipping. You can use this with any dmm...even the free ones from Harbor Freight.
http://www.amp-head.com/product_info.php...ucts_id=30

First measure the plate voltage:
Put the probe into the amp and then the tube into the probe.
Set your probe to measure mV.
Set your dmm to 200 mV DC.
Turn on your amp and leave it in standby for a min or so.
Then give your amp power.
Write down the mV reading...that is your plate voltage at idle.
Put that plate voltage and power tube type into this calculator:
http://www.ax84.com/biascalc.html


Adjusting the bias itself:
Bring the amp back to standby. Maybe even off to be totally safe but I dont think its necessary.
Change your probe to measure the bias mA.
Set your dmm to 200 mA DC.
Turn the amp to standby for a min.
Then turn it on.
Read the dmm and adjust the trimpot until the amp reads between 60%-70% from the webpage chart. Personally I go between 60%-65%.
Turn everything off.
Remove the probe.
Since the rd45 does have 2 trim pts go back and forth a few times measuring the current n each tube. Adjust until they are very close.
 
nico22":175aseri said:
i am not opether from GAB sorry.
Saw its rd45 is at 440v too.

Find it is pretty big difference...

Would be great to know the ''standard'' factory plate voltage.

BTW, I asked music corp the max dc bias current the OT can handle, here what they answered : I'm very sorry but those specs are for internal use only and are not available to the public :aww: :thumbsdown:

they just say factory bias is 35 ma, but don't know for what voltage, gonna ask them.
Click to expand...


As you mentioned mine does seem a bit high. And yes I asked if you were opether because you both measured at 440. Come to think of it, it seems that most of my amps run a high plate voltage when compared to others. Maybe my probe is bad or my house's voltage is higher. I believe I measured the house not too long ago and it was 119 at that time. I'll have to look into it more or measure with a different method to see if the probe is bad.

Hmmm...35mA almost seems a bit high for a factory to kick out an amp with. But maybe...

EDIT: I just measured the house again really quick before bed and I'm getting between 118.8-119.3V...I'll keep investigating. Nico22, have you measured the voltage from your wall that this amp is plugged into (just curious)?


Jeff Hilligan,
Did you happen to take a reading or play with the bias on this amp by chance? Just trying to get a baseline. Thanks.
 
nico22,
What country are you in? I know houses in the USA get 240V but it is then split to 120V except for certain outlets used to larger appliances.
 
That may very well explain why our readings so are different. I see opether in in the USA. But you are saying your plate voltage is at 480 now right?
 
yeah i know that strange :confused:

With stock ruby, it was 440v (if my dmm was alright, or my eyes :LOL: :LOL: ) and 40ma

With TAD, 490v and 32ma beforecorrecting the bias to about 41 ma
 
Did some measures with my RD45

TAD 6L6GC STR : 494 V plate, -52 mV input grid, 42 mA

Then I changed nothing, just swapped to 6L6 stock Ruby : 487 V plate, -52 mV input grid, 50 mA

Played them only with rythm metal, same settings : TAD are warmer, highs are "harder" with Ruby, so they sound little more percussive...Both brands are good for me, just different taste.

I'll try later with leads
 
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