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THE AM BULLETIN BOARD => Technical Forum => Topic started by: w4ax on April 11, 2024, 05:50:22 PM



Title: Suggestions: 3CX3000A7 grounded cathode grid driven amp
Post by: w4ax on April 11, 2024, 05:50:22 PM
Has anyone successfully grid driven a 3CX3000A7 on 40M? I am close to achieving success but currently have a mechanical issue with my pi output vacuum variable loading cap (yes, I know a VV is overkill).

I am using the input circuit from the Collins 21E AM transmitter with frequency dependent components reworked for 40M. Instead of link coupling I am using a variable capacitor to couple from the exciter.

Attached is the input circuit. Here are pictures of the amp in progress:
https://photos.app.goo.gl/qfL4JDMz1XtGii2X8

Yes, I know grounded grid would be easier. I have another 3CX3000F7 that is ground grid.

Id really appreciate seeing your input circuit or suggestions for a grid driven 3CX3000. Thank you in advance.


73,

Mack
W4AX


Title: Re: Suggestions: 3CX3000A7 grounded cathode grid driven amp
Post by: KD1SH on April 11, 2024, 06:51:35 PM
 Very impressive construction; looks like many months, at least, in the making. What is that big high voltage connector? It looks like an SHV type, but bigger.


Title: Re: Suggestions: 3CX3000A7 grounded cathode grid driven amp
Post by: KL7OF on April 11, 2024, 09:36:50 PM
very nice.. I have no advice for you as I have never grid driven a 3x3 tube....  I would like to try a grid driven 4x5 tube if I can get around to it.   
   Did you wind the plate choke?  .. What are the sPecs on the parasitic plate suppresor?  Is it standard for a low band 3X3? 
  Again     very nice ..good luck ...I hope to hear you on this rig..  Steve


Title: Re: Suggestions: 3CX3000A7 grounded cathode grid driven amp
Post by: W3SLK on April 12, 2024, 09:58:22 AM
Ken, W2DTC built 2 3CX3000F7s, (the F designation doesn't require a socket). He did a helluva job on them too.

http://w2dtc.com/
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