M60 Plate Voltage & Bias (on the cold side?)

adr1anos

adr1anos

New member
Hello friends,
I recently purchased an Elmwood Modena M60 and I wish to congratulate the guys from Elmwood for an excellent product!

I would like to discuss the amplifiers settings with the more knowledgeable of you regarding your Elmwood Modenas.

I used a TubeTown Bias probe and I measured the Plate voltage at 425v (pins 3 to 8) and the Bias Current (after a thorough warm up) at 30mA.
This seemed quite on the cold side to me, so I raised the Bias to 35mA.

Any thoughts? Are your M60's at similar levels?
Have you noticed any tone improvements at any particular Bias levels?

All ideas and input you care to share will be especially welcome!
Cheers!
 
This would not be specific to the Elmo. This applies to any tube amp. Based on your plate voltage 25/425= .059 x .70= 41ma which would be 70% maximum plate dissipation at idle. Personally I bias around 63 to 64% which would be 37 or 38MA for your amp. :thumbsup:
 
I've never checked mine yet since I didn't have to change the tubes yet...I'm going to pull her apart and see what mine is biased at. I'll bring it up to around 60-65% if its low and see how the sound changes...
 
adr1anos":185kelz8 said:
Hello friends,
I recently purchased an Elmwood Modena M60 and I wish to congratulate the guys from Elmwood for an excellent product!

I would like to discuss the amplifiers settings with the more knowledgeable of you regarding your Elmwood Modenas.

I used a TubeTown Bias probe and I measured the Plate voltage at 425v (pins 3 to 8) and the Bias Current (after a thorough warm up) at 30mA.
This seemed quite on the cold side to me, so I raised the Bias to 35mA.

Any thoughts? Are your M60's at similar levels?
Have you noticed any tone improvements at any particular Bias levels?

All ideas and input you care to share will be especially welcome!
Cheers!
Click to expand...
So? Did you notice a change?
 
I did not have the stock values in place long enough for me to really get used to the sound and notice a difference.
I plan to do extensive listening tests, as soon as I have some playtime with the unit and can objectively notice subtle changes.

I am interested in other M60 user's amps stock values for Plate Voltage and Bias current, just to compare notes.
Please offer your own, if you have taken any measurements.
 
Well get this! I opened up my M60 last night and got a B+ reading of around 450VDC....its was biased at 20ma!!!!!!!!!
I always thought the sound was a little on the cold side and blamed it mostly on the speakers and or pickups.
Well there you go...I brought the bias up around 36ma and its sounds SOOO much smooth and warmer!!!!
 
I'm just wondering why the bias would be so off with an amp like Elmwood???? Jesus, you would think they would set it up better than that when it leaves. It couldn't have drifted that much....its a brand new amp! :confused:

Oh yeah and BTW...its a pain in the ass to bias. First I had to find the bias trim pot which was hidden behind a tier of trace board so you have to unscrew that to get to it. No pin numbers on the main trace board under the tube socket. Just little stuff but a pain none the less. External bias points go a long way in a well built amp or at least easy access to the bias trim pot if you have to take the chasis out!!!
 
That was very low. They all usually bias low. Thier is a warranty on the tubes usually for six months. They hope most people will not check so they get through the warranty period. Whenever I get an amp, new or not, I open it up and test all power tubes for shorts. Sometimes they get shaken up in shipping. Better safe than cooking an OT if the fuse doesn't do it's job. Bet it sounded so much better.
 
Well she's officially 6 months old now so I can crank the bias where it should be and get her moaning like she should!!! :D
 
I am very glad to hear that my unit was not alone in being biased so cold.
I took the measurements to have a factory reference before I started fiddling with my own, but , I am also surprised that they choose such cold settings for a factory adjustment. Emphasis on tube reliability I presume..

Yes it is a pain adjusting the bias, removing boards to get to the pot, but it is worth it I think, aiming at one's own personal preference.

I have several pairs of tubes to try out, and I will in the future do a proper tube test for both pre and post tubes.
(I did exactly that for my Cornford Roadhouse 30, check out my Tubes Review if interested:
Review of Pre and Pw Valves for the Roadhouse 30

But I am very curious to hear the amp with a pair of cranked tubes, maybe to 40-45mA bias to see how the tone character develops!..
 
These values look to be right on the money.
This is your own/your techs values, or did the unit come with these? Also, how old is it?

Anyway, from the posts so far it seems that some inconsistency is being observed regarding default bias factory adjustment of the Μ60's..
Therefore, checking and properly biasing M60 Elmos, even brand new units, may be the indicated practice!
 
Does the unit still have the original tubes?
If the tubes were changed, then it is very likely that the previous owner had the amp properly rebiased.
This could explain your very good settings..
 
Don't know, sorry. V1, V2 and V3 have "Elmwood" printed on them, therefore i think these are original tubes. But V4 is a Sovtek, that might be an indication that tubes have been changed. Power tubes are not labeled but they look exactly like the EL34 that Tube-Town sells under their own brand (just without the TT-logo printed on them), if that helps.

See a picture here

http://www.tube-town.net/ttstore/produc ... ching.html

I have the TT tubes here so i can compare them directly and its 100% the same tube.

Anyway, I did some tube testing today and here is what i like best:

V1 SED 12AX7 (C-Logo)
V2 Tung-Sol 12AX7
V3 Tung-Sol 12AX7
V4 Sovtek 12AX7WA (didn't test other tubes here, had no time)
V4+V5 Tung-Sol EL34B

The amp had a bit of an annoying mid range emphasis and bass was not stable and bit muddy. The problems are all gone with the setup above, the amps sounds really great now. Expecially changing V1 and V2 helped a lot.


EDIT: I took another look at the original power tubes, they are the original power tubes from Elmwood as they carry an Elmwood stamp. Somehow I missed that stamp, sorry.
 
Well, this is all very interesting..

M60's come with a Sovtek especially in V4, it was also verified in an interview of Elmwood (I think it was Jan) so these were all original tubes, in your unit.

Very interesting results of your sound tests and tube choices also! As you may see in the Review I posted here earlier, I am very pleased with the Tung-Sol EL34Bs and they were my own final choice, I am glad you also found them pleasing.

I have my full tube set ready and waiting and I will proceed with the swap, as soon as I have some playtime with the amp and its factory tubeset and can objectively notice subtle changes.

Thank you for posting your findings, quite helpful indeed.
 
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