Hi all, I built an Ampeg SB-12 with 2-6v6,tied screens and plates together, used the Jim Kelley tone control values -love that big clean. I would like to try another one in an old project amp that is ready for 4-el84. The Hammond 1750F power transformer is listed at 173ma. The OT is a Heyboer Bandmaster with 4K impedance. Is the amp design suitable for 4-EL84? If not I could use 2-EL84s and use the 4 ohm tap into a 8 ohm speaker hoping to get 8K impedance .
Any advice would really be appreciated. Thank you.
SB-12ish question
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Re: SB-12ish question
4k is ok at roughly 320v at the plates, depending on bias. 173ma is too little for a hot, ac30 style bias but it may work for a different application.
are you speaking of the https://www.evatco.com.au/372fx-power-transformer or the 1750f output transformer?
are you speaking of the https://www.evatco.com.au/372fx-power-transformer or the 1750f output transformer?
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Stevem
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Re: SB-12ish question
4K will work just fine with 4 EL84s.
On a side note I would fuse the center tap of the OT.
Other then JJ brand EL84s these new manufacture tube tend to blow often, with the failure taking place the next time you power up the amp after running it hard.
On a side note I would fuse the center tap of the OT.
Other then JJ brand EL84s these new manufacture tube tend to blow often, with the failure taking place the next time you power up the amp after running it hard.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: SB-12ish question
My error. The PT is a Hammond 270FX 550v CT 173ma ss rectifier
I have fixed bias. If I don't like it with EL84s I can manipulate the Heyboer to see 8K or use a Hammond 1750F (7.6K) and use 2 6v6s.
Thanks for your time advise.
I have fixed bias. If I don't like it with EL84s I can manipulate the Heyboer to see 8K or use a Hammond 1750F (7.6K) and use 2 6v6s.
Thanks for your time advise.