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In Reply to: RE: No this is not an comersial product posted by pix on April 03, 2017 at 22:59:28
"even though not carbon composition I think they are suitable for this application."No, they're not. Only carbon composition is suitable for use as a grid stopper. All others risk creating oscillation that can be difficult to identify and troubleshoot.
No reason to have a 25K input Z. Remove the network and install a 100K pot to ground at the grid. Also, if you're interested in a pentode front end, the EF86 is one of the best. Internally shielded, stable, low distortion, minimal microphonics, etc. I won't use anything else.
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Buy Chinese. Bury freedom.
Edits: 04/04/17Follow Ups:
Ok. I will change to carbon composition resistors.
Due to the input network I have a 100 K stepped ladder switch too try.
How high does the grid leak need to be for the E280F in triode mode?
I'm not familiar with the E280F specifically, but 100K is a safe value for a grid resistor.
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Buy Chinese. Bury freedom.
For the input stage( or any other, for that matter), as low as possible w/o adversely effecting the preceding stage. I like a linestage that can drive low loads...and for amplifiers, have run the grid resistor as low as 8kOhms on its input stage. Makes for an interesting linestage testing rig; few will work well like that...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
There are lots of good pentodes to use *AS* pentodes. The lower gm and plate dissipation of the small, nominally 'signal' ones require a fairly high value plate load resistor to deliver adequate gain. When working into the grid of a power triode, it is not only the Miller of the voltage amp, and its loading from the volume pot, but the Miller-amplified capacitance of the final you'll have to worry about.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
So, what you are saying is that using the 6B4G as a penthode could cause drive loss compared to use it as a triode?
Or do you mean if changed to another driver tube?
I don't think it is possible to use 6B4G as a pentode( though arranging them in Cascode is perhaps possible ). The late production 6AV5 Sylvania tubes were sold as 6B4's and I do not know where the connection of g2 to anode was made.
There are lots of small and medium-sized pentodes to use for voltage amplification. Try a small TV sweep tube...:)
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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