Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: goldstache on February 07, 2016, 01:08:58 pm
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Starting a new build and was looking for a single triode tube, either 7 pin or 9 pin, to use for the trem LFO. I could use a 12ax7, but don't want to leave a triode stage unused. Hurts my heart. hahahaha.
Also, figured I'd ask here and maybe learn something! Im planning on having it wiggle signal to power tubes.
Looking forward to your replies!
thanks
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6AV6 or 6AT6 would work to replace a single triode in a 12AX7. Just ignore the two diode connections.
If you will be wiggling 6L6s or other similar big tubes I recommend using a 12AX7 and the Fender 6G16 circuit.
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Thanks Sluckey!
Im planning on wiggling some el84's
Similar to Kalamazoo model 12. Signal amplitude modulation, rather than bias wiggle. I am gonna try a AB763 style reverb circuit though.
Any pointers?
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You could use a MOSFET for the wiggler stage. It's not in the signal path. I know I've seen a schematic using an LND150 for tremolo recently, just can't recall at this moment. Virtually a direct drop in for a tube triode, but no heater current required. No funky single triode tube to worry about sourcing either.
Forgive my heresy, but even Randall Aiken has amended his website to add:
Q: Is solid-state really as evil as you say?
A: Yes. Update: I'm becoming rather fond of the new breed of high-voltage depletion-mode MOSFETs, so I may change my mind about this...
Respectfully,
Chip
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Ive used that LND150 for an effects loop drop in. Worked pretty well. Maybe I'll give it a whirl.
Thanks!
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Resurrecting an older thread as I'm interested in using LND150's in my Hoffman single channel AB763 tremolo section. I believe the Trem is a 6G16 circuit? I'm thinking it would need some changes to the bias, but otherwise the LND150 should drop right in. I haven't been able to find much info on biasing the LND150, or many details from people who have done the swap. Anyone out there got hints please?
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I drew this up some time back and have never built it, but I think it would work? I have used mosfet CF's in numerous builds with success.
IF you are open to a single tube that is a pentode, the 6AU6 used for tremolo on Silvertone 1482 and DanElectro Centurian makes for a great tremolo sound, IMO. I've owned a Centurian, Princeton Reverb and VibroChamp all at the same time and the Dano Centurian easily had the best sounding tremolo to my ears.
http://el34world.com/charts/Schematics/files/silvertone/Silvertone_Schematics.htm (http://el34world.com/charts/Schematics/files/silvertone/Silvertone_Schematics.htm)
The 6AU6 tremolo was even used by DanElectro on amps with 6L6's on the Commando and Challenger amps.
http://el34world.com/charts/Schematics/files/danelectro/Danelectro_Schematics.htm (http://el34world.com/charts/Schematics/files/danelectro/Danelectro_Schematics.htm)
With respect, Tubenit
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I could use a 12ax7, but don't want to leave a triode stage unused.
I like the suggestions by Sluchey and Tubenit (6av6 - 6au6)
But if you use a 12ax7 isn't implicit that you have an unused triode
(http://www.thevintagesound.com/ffg/schem/champ_vibro_aa764_schem.gif)
Franco
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OK, I'm going to announce a pet peeve: asking for advice "in a vacuum" - no schematic. For this thread, critical info is missing: type of power amp tubes; voltages; preamp topology.
Power tube bias trem is OK with small bottles (like 6V6), but has been largely abandoned for big bottles (like 6L6). For the latter a larger voltage swing is needed. For big bottle power tubes, usually trem is applied to a preamp tube. All this affects the design of the trem circuit.
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If you are building towards the K Reverb 12, why not just build the same way. The amp has plenty of verb and a great tremolo. You mentioned EL84's.
I owned one of those and sold it to a close friend, so it is not gone too far. Of course you can tweak any signal how you wish, I am just speaking of the tremolo and reverb. These amps get bright and they had a cheap speaker, but that is easy to fix.
So yea, I guess it depends, but I will say the K 12 Reverb is a full featured amp that gets overlooked sometimes.
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Sorry. Should have included a schematic.
As you can see, it's a bias wiggle tremolo circuit. I want to use cheap LND150 transistors instead of a rather more expensive 12AX7 (in the red circle). Do I need to change the bias resistors in the schematic if I drop in the transistors? I think I do. But I don't know how to bias them, and my google search efforts have not found anything helpful. Any helpful tips would be greatly appreciated.
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You could try this.......
(http://i761.photobucket.com/albums/xx254/Timbo-08/001%204_12.jpg) (http://s761.photobucket.com/user/Timbo-08/media/001%204_12.jpg.html)
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> You could try this.......
Missing ground at 12V Zener will kill the JFET.
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It is strange, my copy show it correctly
(http://i.imgur.com/M4SiER4.jpg)
Franco
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OK, SORRY, I wasn't able to resist
:l2: :l2:
it was a joke, I corrected the image
Franco
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Thanks Kagliostro! I'm such a tube snob I didn't know SS components could run on "tube" voltages -- off B+ supplies in the 200V - 300V range. That makes SS reverb & trem easier to implement in a tube amp. E.g., geofex.com has a SS trem circuit that needs a string of zeners to knock down the supply voltage.
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This was posted yrs ago on the forum. I remember the guy stating that the tremolo worked to his liking.
With respect, Tubenit
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> didn't know SS components could run on "tube" voltages
MOSFETs are commonly available in 100V, 500V, even 1,000V ratings.
This one may be 450V? Whatever, pretend it is.
Note this is higher than 12AX7 or 6V6. (However a 6V6 won't die right away at 475V. The MOSFET could, or could work an hour or a month then die.)
This plan uses a JFET which now only come to 30V-40V rating. However the MOSFET Gate is nailed to +12V from a Zener (if you have the right plan). I think an IRF820 is enhancement mode? (Never mind.) So its Source will be at 14V or 16V. That puts 13V or 15V across the JFET, well short of its likely rating.
MOSFETs are typically "big" (high input capacitance) and hissy. Here both aspects are dominated by the small quiet JFET. The MOSFET is just doing heavy lifting to hundreds-Volt signal and supply.
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Ciao JJasilli
I haven't deserves, was TIMBO that posted the schematic with the Mosfet
Only I read the post from PRR and corrected a version of TIMBO's schematic I had on my archive (as a joke)
if there is someone that deserves, is TIMBO
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Here the project story of an amp with a proven mosfet tremolo
http://www.mediafire.com/file/aflnirflqgrftm6/mikede30.pdf (http://www.mediafire.com/file/aflnirflqgrftm6/mikede30.pdf)
Franco
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YOU GUYS :happy2:
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:occasion14:
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use a 12AX7 with both sections and employ the most luscious trem. one can build.
please click me! (http://el34world.com/charts/Schematics/files/fender/Fender_tremolux_6g9_d-fa.pdf)
click me too! (http://el34world.com/charts/Schematics/files/fender/Fender_tremolux_6g9b_schem.pdf)
--pete