Quick bias question. 6CA7 and EL34's.

[eyeball987]

I had all Winged C 34's in the RM100 biased up between 30 and 31. I just dropped in a set of 6CA7's and am really liking the results after day 1. I now have all of them at just over 31.

According to the manual, I am in range on the cooler side. Based on some numbers that Julia posted years ago I am on the warmer side. Any new thoughts on whether I can go a little hotter or should I stay where I am at?

 

[eyeball987]

FWIW, the 6CA7's are JJ's.

 

[eyeball987]

What is the plate voltage on the RM100KH anyway? Is it really up in the lower 500 range?

I am going to set the 34's and 6CA7's at 33mA tonight and call it a day if it sounds any better than where I am at 31. If not, I will cool them back down and enjoy the longer life.

 

[Jaded Faith]

I typically bias my EL34-type tubes around 36-38mA, as I prefer them a touch hot. The last time I measured and RM100 I think it was around 480V on the plates. Using that to calculate ideal bias:

Wattage/Plate Voltage = Max Plate Current Draw at Idle

25/480 = 52mA

To set it at 70%:

52*.70 = 36.4mA

If you prefer it cooler, just plug the lower percentage into the equation in place of the .70 to get a new value.

 

[eyeball987]

I typically bias my EL34-type tubes around 36-38mA, as I prefer them a touch hot. The last time I measured and RM100 I think it was around 480V on the plates. Using that to calculate ideal bias:

Wattage/Plate Voltage = Max Plate Current Draw at Idle

25/480 = 52mA

To set it at 70%:

52*.70 = 36.4mA

If you prefer it cooler, just plug the lower percentage into the equation in place of the .70 to get a new value.

Perfect! Thanks for the info. I was basing my numbers on a plate voltage of 515 that I picked up from an old thread on here. I know nothing about that stuff.

34mA will be the number I start with tonight.

 

[eyeball987]

Bumping the bias a bit made the tone better. I am set at about 33.5mA on each tube now and I was digging it pretty hard.

Might be my ears but I had to up the treble a touch. That was after a couple hours with the master at 11:00 and the module volumes at 9:30 in a 12X15 room.

Hey Fig! Where do you set your bias with the 34 / 6CA7 mix?

 

[Mattfig]

Bumping the bias a bit made the tone better. I am set at about 33.5mA on each tube now and I was digging it pretty hard.

Might be my ears but I had to up the treble a touch. That was after a couple hours with the master at 11:00 and the module volumes at 9:30 in a 12X15 room.

Hey Fig! Where do you set your bias with the 34 / 6CA7 mix?

I set both at about 37...The ones I buy have a pop-up timer to let me know when they're done...

 

[eyeball987]

I set both at about 37...The ones I buy have a pop-up timer to let me know when they're done...

Holy heat batman! Do you burn through them quickly or am I just scared of burning something up?

 

[rblyn]

I had all Winged C 34's in the RM100 biased up between 30 and 31. I just dropped in a set of 6CA7's and am really liking the results after day 1. I now have all of them at just over 31.

According to the manual, I am in range on the cooler side. Based on some numbers that Julia posted years ago I am on the warmer side. Any new thoughts on whether I can go a little hotter or should I stay where I am at?

I LOVE the Winged C's EL34's by the way. So **** crunchy but I'd rather pair them with some KT88's for additional BALLS...but in terms of bias, Ive been using 60% as my baseline only after talking tubes and tone with Trace at Voodoo. 70% is definitely talked about as the standard as Rob writes and its all a matter of taste but Trace mentioned his pros (and most guitarists he works with) like the the feel and sound of 60%. Once I tried that, I agreed 8) At 60%, you're talking about 31 or 32ma for 34's.

That's one of the great things about the RM's- You can bias it yourself, work through different sets and see what's best for YOU. Love the flexibility.

 

[eyeball987]

but in terms of bias, Ive been using 60% as my baseline only after talking tubes and tone with Trace at Voodoo. 70% is definitely talked about as the standard as Rob writes and its all a matter of taste but Trace mentioned his pros (and most guitarists he works with) like the the feel and sound of 60%. Once I tried that, I agreed 8)

I guess that I am at about 60% between 33 and 34. Probably pretty close anyway. Sounded great to me last night. I put some more hours at that setting this week and see how I continue to feel.

 

[Jaded Faith]

I'll often set it by feel and response as the ultimate determining factor. As mentioned, 60-70% is a standard range. What I'll often do is start at 60% and then change it around while playing with my meter still hooked up. At the end of the day, it's the response between me and the amp that matters most. There's no right or wrong and what works for one may not work for another. Don't be afraid to experiment.

 

[Mattfig]

I set both at about 37...The ones I buy have a pop-up timer to let me know when they're done...

Holy heat batman! Do you burn through them quickly or am I just scared of burning something up?

I do the same as Rob and go by feel....I tend to go toward the hot side of any Britishy (I know that isn't a real word) tones...With 6L6s thru 6550s and more I tend to go toward the cooler side as the glass gets bigger...

I don't blow through tubes as fast as you would think...I'm lucky to have an old tube tester that can confirm what my ear tells me is a worn tube - and that is about every 6 months...Not bad...I don't buy expensive power tubes as I find I actually prefer the tone from middle of the roaders...Running them hot is not at all a budget killer and it sounds right to me...There are things that get burned up in my home studio regularly...They just aren't tubes... :wink:

 

[eyeball987]

I haven't been able to play again since I upped the heat to 33.5. Tonight I am going to get crazy and bump it up to 35mA!

I am feeling more confident now that I have a backup set of Winged C 34's and I may have just set up a trade for a back up set of 6CA7'a. I should keep some fuses on hand though. Time to hit the search feature.

 

[Anomaly]

Okay, so I got my EH 6CA7 tubes today.. They won't stay balance(?) bias at the same time? When I moved the pot clock-wise on the right, left tube seems to move up too? Same effect the other way around? I'm sitting at 31 & 35mV's.. Don't have this problem on the stock Ruby 6L6's, those balanced easily. Could I possibly have a mis-matched pair? Sounds great though, more mid grit at low volume.

 

[Jaded Faith]

Okay, so I got my EH 6CA7 tubes today.. They won't stay balance(?) bias at the same time? When I moved the pot clock-wise on the right, left tube seems to move up too? Same effect the other way around? I'm sitting at 31 & 35mV's.. Don't have this problem on the stock Ruby 6L6's, those balanced easily. Could I possibly have a mis-matched pair? Sounds great though, more mid grit at low volume.

Modern marketing from tube companies and resellers would like you to think the pair you have is poorly matched. I personally feel any readings within a value of 5 from each other is just fine. Remember for years many of the legendary amps were equipped with the first few tubes that were grabbed from a shelf and matching wasn't even a concern. In reality, they operate in circuits that aren't flawless themselves and I wouldn't doubt they sound fantastic.

My personal reference point for tubes starting to go is when a "matched set" starts to read a spread of 7 or higher. That's usually a good indicator one of them is on it's way out soon.

 

[Anomaly]

Okay, so I got my EH 6CA7 tubes today.. They won't stay balance(?) bias at the same time? When I moved the pot clock-wise on the right, left tube seems to move up too? Same effect the other way around? I'm sitting at 31 & 35mV's.. Don't have this problem on the stock Ruby 6L6's, those balanced easily. Could I possibly have a mis-matched pair? Sounds great though, more mid grit at low volume.

Modern marketing from tube companies and resellers would like you to think the pair you have is poorly matched. I personally feel any readings within a value of 5 from each other is just fine. Remember for years many of the legendary amps were equipped with the first few tubes that were grabbed from a shelf and matching wasn't even a concern. In reality, they operate in circuits that aren't flawless themselves and I wouldn't doubt they sound fantastic.

My personal reference point for tubes starting to go is when a "matched set" starts to read a spread of 7 or higher. That's usually a good indicator one of them is on it's way out soon.

I put pack the old Ruby 6L6's and those match perfectly at 35mV, tried the EH 6CA7 again, now there value's are 7mV's (31/38mV) apart? I like the way it sounds though :lol:

Ebay seller agreed to exchange them, I hope he sends me a better match pair. always appreciate sharing your knowledge thanks Rob!

 

[eyeball987]

I put pack the old Ruby 6L6's and those match perfectly at 35mV, tried the EH 6CA7 again, now there value's are 7mV's (31/38mV) apart? I like the way it sounds though :lol:

I agree! I am digging the 34 / 6CA7 mix.

I have been lucky though. Other than a really old set of 34's that starting running all over the place on the bias map, I have been able to keep pairs within 1mA. Same goes for the 34 / 6CA7 mix loaded up now.

 

[Anomaly]

Sending them for an exchange. Hopefully the next pair are "match" or at least not more than 5mV apart :lol:

That fat mid gritz from 6CA7 is haunting me know.

 

[eyeball987]

That fat mid gritz from 6CA7 is haunting me know.

I hear that! I just shipped off a pair of 6550's in a trade for a second set of the 6CA7's to keep as a back up. 34's and 6CA7's are my new favorite tone set!

 

[Rod]

Thanks for all the bias info guys. I just had to replace my Gold Lion reissue Kt66's after a year in my RM50 cause 1 was reading 30ma and the other was at 60!!! Talk about a mismatch... Went back to KT77's..... more my tone