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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 11:10 pm
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Whatever you say, einstein.

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Have a nice......whatever.

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 11:37 pm
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Yeah Bill!!! Heads are a different story. There's no way for a lazy maneuver with my B'Master. BTW That's a sharp looking- compact amp. Reminds me of my Clubman 35. Art

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Post subject: Re: 1965 Pro Reverb
Posted: Mon Oct 28, 2013 3:28 pm
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BMW2002Ti wrote:
Advice: keep those Tungsol 5881/6L6WGB biased around 15 watts per tube. Approx 31mA per tube at 475VDC on the plates.


25:475=0.0526 x 0.5 = 0.026A

Curious if biasing at 50% would be a bit cold?
The plan is to start with 50% and go to 60-70% to see what sonic changes this will trigger. Ones ear is the best judge I'd say. :D


Last edited by Nikola Tesla on Mon Oct 28, 2013 5:51 pm, edited 1 time in total.

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Post subject: Re: 1965 Pro Reverb
Posted: Mon Oct 28, 2013 5:16 pm
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Original TS 5881/6L6WGB max at 19 watts. 15 watts = 78%.

They are tough enough to be biased this high. If 12-13 watts sound ok... go for it.

http://www.retrovox.com.au/tsol5881.pdf


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Post subject: Re: 1965 Pro Reverb
Posted: Mon Oct 28, 2013 5:45 pm
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:oops:

Oooops .. I thought all 6L6 tubes are 25W, but obviously not. :D


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Post subject: Re: 1965 Pro Reverb
Posted: Tue Oct 29, 2013 6:22 am
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NT, actually no 6L6 variant maxes out at 25 watts, that I know of...

Metal can 6L6 = 18-19 watts, with max plate voltage = 400VDC

The Holy 6L6GA max is 18-19 watts per tube (Class AB1, push-pull).

6L6GB and the 5881 = 19 watts. (TS 5881/6L6WGB, max plate voltage = 450VDC, but more like 500VDC, in practice)

6L6GC = 30 watts

7581A and KT-66 = 35 watts


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Post subject: Re: 1965 Pro Reverb
Posted: Thu Oct 31, 2013 10:56 pm
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This is what I came up with measuring the amp's bias (1st 5881).

According to this calculator it seems fine (ideal) :mrgreen: .
http://www.webervst.com/tubes1/calcbias.htm

.. but still there are some unanswered questions in this :?: :?:


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Post subject: Re: 1965 Pro Reverb
Posted: Fri Nov 01, 2013 12:53 am
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.. and second 5881 (with tilted wing)

.. quite a different reading :twisted:

If it matters (and probbaly doesn't), this is measured while the amp was on a step down tranny. :P


Image





.. and after 10 min in play position this reading :?: :?:


Image


Weird, isn't it :?: :?:


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Post subject: Re: 1965 Pro Reverb
Posted: Fri Nov 01, 2013 2:40 am
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BMW2002Ti wrote:
NT, actually no 6L6 variant maxes out at 25 watts, that I know of...


6L6GB and the 5881 = 19 watts. (TS 5881/6L6WGB, max plate voltage = 450VDC, but more like 500VDC, in practice)



That's not what the max ratings say on page 1 of the data sheet you provided says:

"Max power dissipation (Triode connection) = 26 watts"

Everything I have read says the 5881/6L6GWB is a 25 watt tube.

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Post subject: Re: 1965 Pro Reverb
Posted: Sun Nov 03, 2013 10:27 pm
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This is still puzzling me, this time both tubes were measured under the same conditions.

Any thoughts as to difference in the bias value?!? :?: :?:

Bad tube or anything else?


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Post subject: Re: 1965 Pro Reverb
Posted: Sun Nov 03, 2013 11:09 pm
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Nikoloa, look like unmatched tubes --- or unmatched grid-to-ground and/or grid stopper resistors.

"Max power dissipation (Triode connection) = 26 watts"


Use this data--- for Class AB1 push-pull.... The Tungsol can easily handle 400-450VDC opon the plate. As long as you keep the wattage around 20watt/tube. Now you can run a 5881/6L6WGB at 25 watts--- but it won't last as long at these wattages.

The 5881/6L6WGB is one of the toughest tube ever made for the military. So, abuse is no issue. You prolly won't get 40 years of life from it --- as some tweeds used to get.

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Post subject: Re: 1965 Pro Reverb
Posted: Mon Nov 04, 2013 7:40 pm
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BMW2002Ti wrote:
Nikoloa, look like unmatched tubes --- or unmatched grid-to-ground and/or grid stopper resistors.

"Max power dissipation (Triode connection) = 26 watts"


Use this data--- for Class AB1 push-pull.... The Tungsol can easily handle 400-450VDC opon the plate. As long as you keep the wattage around 20watt/tube. Now you can run a 5881/6L6WGB at 25 watts--- but it won't last as long at these wattages.

The 5881/6L6WGB is one of the toughest tube ever made for the military. So, abuse is no issue. You prolly won't get 40 years of life from it --- as some tweeds used to get.

Image


BMW,

I disagree with the information you are providing.

The table you are showing above clearly states that it is for TWO tubes, not a single tube. You do not base bias values and max plate dissipation on that.

The maximum design values are shown on page 1 and the tube is listed as 25/26 watts maximum plate dissipation depending on configuration. That is the value that should be used, not 18 watts. Both the 5F6A and Marshall JTM45 used 5881s and they were 40-45 watt amps.

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Post subject: Re: 1965 Pro Reverb
Posted: Mon Nov 04, 2013 8:25 pm
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Bluesky,

OK... but that is triode connection, without Class or tube type.

I've been told to use push-pull, AB1 data. If 25 watts works for you, go with it. Like I stated the 5881 is a super tough tube, so have no doubt that it can withstand those levels of plate dissipation.


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Post subject: Re: 1965 Pro Reverb
Posted: Mon Nov 04, 2013 11:02 pm
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BMW2002Ti wrote:
Bluesky,

OK... but that is triode connection, without Class or tube type.

I've been told to use push-pull, AB1 data. If 25 watts works for you, go with it. Like I stated the 5881 is a super tough tube, so have no doubt that it can withstand those levels of plate dissipation.


BMW,

Since when does one use a specific circuit configuration for the purposes of determining maximum plate dissipation? The tube chart I posted shows the maximum ratings for the 5881 to be 23 watts (no configuration stated but assumed to be pentode) and 26 watts for a triode connection.

Here is the data sheet for a 6L6GC. The AB1 ratings for two tubes are given as 26.5 watts, 18 watts, and 55 watts. Why would any one of those be chosen for the purpose of determining max plate dissipation for what we all know is a 30 watt tube (as shown on page 1 for either a triode or pentode configuration). We're talking about the value to be used when calculating % of max plate dissipation for biasing a tube, not the actual output of the amplifier itself.

http://www.google.com/url?sa=t&rct=j&q= ... 0276,d.cWc

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Post subject: Re: 1965 Pro Reverb
Posted: Tue Nov 05, 2013 2:24 am
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I believe that the total dissipation depends on the configuration of the tube. Triode strapped tube will make different power than in a pentode mode. A push-pull amp will max-out at a different amount than a single-ended. Class "A" differs from Class B, etc.


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