Similiarities to Western Electric
- Thread starter tim273
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It's interesting that they are using parallel feed iron.
To get 20 watts out of a 300B, you'd have to run it at maximum voltage and near maximum plate dissipation and drive the grid positive. This is a decision that will come at the expense of tube life.
To get 20 watts out of a 300B, you'd have to run it at maximum voltage and near maximum plate dissipation and drive the grid positive. This is a decision that will come at the expense of tube life.
Here is what the old WE datasheet said on the subject.
I'm actually building a high power 300B amp for a local customer who wanted something a little different, and I warned him to always have a spare set of 300Bs on hand and not to expect a whole lot of life if he pushed the amp hard.
On the positive side, if you assume the possibility of pressing into A2 at higher powers, you can load the 300B with a 5K output transformer and get really nice overall performance and the high power.
I'm actually building a high power 300B amp for a local customer who wanted something a little different, and I warned him to always have a spare set of 300Bs on hand and not to expect a whole lot of life if he pushed the amp hard.
On the positive side, if you assume the possibility of pressing into A2 at higher powers, you can load the 300B with a 5K output transformer and get really nice overall performance and the high power.
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Deke609
Guest
Paul Birkeland said:
From the WE website blurb: "Class A3 parallel feed single-ended triode topology"
What on earth is "Class A3"? Some middle ground between A2 and AB?
It will be interesting to learn more about how the amp's "Microprocessor controlled bias" works.
cheers, Derek
Paul Joppa
Moderator
So far, it's all marketing-speak. My guess is that their "steered constant current source" approaches push-pull with a dynamically-varying "constant" current. There's an old engineering joke about dazzling with detail vs. baffling with bulls@#t, which is probably relevant here... :^)
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Deke609
Guest
Hah! I think for marketing, the saying might be restated as: baffling with detail (no sale) vs. dazzling w/ BS (great success!) 
This is an approximation of how I'm doing it. Most of the bias voltage appears at the grid from a negative supply and the CCS between filament and ground provides the rest. This will keep the tube optimally biased until it's super dead. This thing is going to eat 300Bs though!
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Thermioniclife
Member
Hey PB, while most of this is beyond me I am curious regarding the last schematic you posted. I see that there are 2 Od3's in series,
I am wondering why this is used, is it because of keeping the cathode current under control by sharing the load between 2 vr's or perhaps the the the high B+ supply? Also I see that you are not using the internal jumpers pins 3 and 7 as a safety or is that not present to keep the sch. simplified? Just askin. Thnx.
I am wondering why this is used, is it because of keeping the cathode current under control by sharing the load between 2 vr's or perhaps the the the high B+ supply? Also I see that you are not using the internal jumpers pins 3 and 7 as a safety or is that not present to keep the sch. simplified? Just askin. Thnx.
The 0D3s just reduce the voltage going to the 6CK4 to keep it from drawing tons of current across the cathode choke. If you pull the 0D3s out, the 6CK4 won't conduct, nor will it pass signal, and the grid bias at the 300B will become more negative, so the jumpers aren't so necessary. The schematic I posted was something I drew out in a couple of minutes and is nowhere near a finished design, more of a sketch of what such an amp might generally look like.
Gerry E.
Member
Just a thought - Maybe they know that their new graphene coated 300Bs are up to the task? When and if the amp ever becomes available I could easily see some type of disclaimer that ends with "... only when used with genuine current production Western Electric 300Bs".Paul Birkeland said:
Gerry
Gerry E. said:
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