Home » Audio » Group Build » questions re 300b group build
questions re 300b group build [message #32194] Thu, 01 November 2007 07:36 Go to next message
duderduderini is currently offline  duderduderini
Messages: 2
Registered: May 2009
Esquire
Hi Damir
I have just discovered this thread and forum. I have stumbled across the concept of driving a 300b with a pentode.
2 questions If I may.
1. Where would i get the 1700 H grid choke? What specs
2. I have the iron for a parallel 300b set ca this driver stage be suitably modified to drive that or do I just use 2 of the 6688 driver stages?
Thanks
Nick

Re: questions re 300b group build [message #32196 is a reply to message #32194] Fri, 02 November 2007 09:59 Go to previous messageGo to next message
real_one is currently offline  real_one
Messages: 55
Registered: May 2009
Baron
Lundahl

Re: questions re 300b group build [message #32198 is a reply to message #32194] Mon, 05 November 2007 15:50 Go to previous messageGo to next message
stewcle is currently offline  stewcle
Messages: 2
Registered: May 2009
Esquire
How critical are the power supplies to the penthode? Do you need to regulate/serious filtering? I dont seem to be able to find the powersupply schematics with this project

Re: questions re 300b group build [message #32201 is a reply to message #32198] Wed, 07 November 2007 18:46 Go to previous messageGo to next message
PakProtector is currently offline  PakProtector
Messages: 935
Registered: May 2009
Illuminati (2nd Degree)
hey-hey!!!,
PSRR of a pentode depends upon what sort of output you're dealing with. In this case it has terrible PSRR, because of the high plate impedance( the plate curves are nearly horizontal). What ever voltage shows up at the top of the plate load resistor, shows up at the plate end too. Now if we were transformer coupled, that behaviour is a plus, because the voltage would not be able to induce a current and w/o current change in the output TX, there is no signal.

IOW, you'll need a clean DC supply for the driver pentode.
Best Regards,
Douglas


Re: questions re 300b group build [message #32202 is a reply to message #32194] Thu, 22 May 2008 04:16 Go to previous message
RC Daniel is currently offline  RC Daniel
Messages: 18
Registered: May 2009
Chancellor
Hmmm, looking at your post, I am gussing you are referring to driving the 300B/s with a pentode *strapped as a triode* - the 1700Hy (grid)choke and Damir's previous threads seem to suggest. If that is indeed the case, disregard the pentode-related suggested below.

Yep, Lundahl can supply 'grid' chokes, as can Magnequest, SAC Thailand (SILK brand), and many other transformer suppliers.

As for driving 300Bs in parallel - quite a task; without doing the calcs, I think it would be pretty borderline... I think you would have some high-frequency roll-off at the operating points suggested, tho don't take my work for it. You could run a parallel driver stage, tho there are probably solutions that are easier to implement and less costly. I wonder what an E180F would sound like with a little more current (and lower plate resistance) - would stand a better chance of driving the parallel output...

Hope this helps in some small way.

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