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 Post subject: 5F1 Build Advice
PostPosted: Mon Jan 07, 2019 8:31 am 
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Recently my nephew and I began building a multi modifications 5F1 amplifier. Some of the mods include a switchable bypass cap on V1. As of now the values we’ve chosen are .68uf, 10uf & the stock 25uf cap. We also changed the 100K plate resistors to 220K and the .022uf coupling caps were lowered to .01uf. There are 2 additional switches. One to disconnect the negative feedback and another to switch in a conjunctive filter across the O.T.’s primary. For the filter values we chose a 10KΩ 5W resistor and a series .047uf cap and placed them across the 8K primary of the O.T.

After initial testing we both decided to return the plate resistors and coupling caps to their stock values. The switched bypass cap mod did all the tone shaping we wanted so lowering the values of the coupling caps didn’t seem necessary. We both liked the additional dirt from the 220K plate resistors but we both agreed that having a little more clean tone available would be the best way to go.

A note on the build: Once we built the amp we did some math and found that the 6V6 plate dissipation was close to 18W. According to my info the JJ 6V6S we’re using is spec’d at 14W. To lower the dissipation we raised the 470R cathode resistor to 606Ω using a 1KΩ 5W wire-wound pot.

Now for my advice question. Vince wanted to know if we could use a different power tube. Since we only built this to be a 5W amp I thought that maybe we could replace the 6V6 we’re using with an EL84? I figure it’s do-able but I have limited knowledge of tube circuits and have no idea how I would go about making the necessary changes. I’d appreciate any input you guys have to offer.

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 Post subject: Re: 5F1 Build Advice
PostPosted: Mon Jan 07, 2019 9:04 am 
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https://www.yellowjacketstc.com

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 Post subject: Re: 5F1 Build Advice
PostPosted: Mon Jan 07, 2019 9:56 am 
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No go. Won’t fit under the hood of the head cabinet.

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 Post subject: Re: 5F1 Build Advice
PostPosted: Mon Jan 07, 2019 10:14 am 
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Stephen wrote:
No go. Won’t fit under the hood of the head cabinet.


Pull the chassis out of the head cabinet.

Give it a test run with the yellow jacket.

If you like it configured that way, do the math and install a nine pin socket in the chassis for the EL 84.

You're going to find that the necessary voltages are a little off but should be in the ballpark.

The yellow jacket should not be viewed as a permanent solution in any case.

I always use them to try things out and then do a permanent change over if I like the sound.

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 Post subject: Re: 5F1 Build Advice
PostPosted: Mon Jan 07, 2019 10:52 am 
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Scooter, would 6K6's be an option for this amp? I'd think that the plate voltage would have to be lowered some and the cathode resistor changed, since this type is only rated for 8.5W of plate dissipation.

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