Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Deric on April 22, 2017, 10:34:13 pm
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I have a failed amp project that I've been looking to do something with. I saw tubenit's post about a HoSo56 Minimalist in this thread...
http://el34world.com/Forum/index.php?topic=21870.0 (http://el34world.com/Forum/index.php?topic=21870.0)
I like this idea! I have a couple of questions though...
Amp is set up using Heyboer 18W transformers. Power supply is using an EZ812 and a 32/32 cap can. Can I use the EZ81 with this design? For filtering I could either use the 32/32 and add a couple caps on the board or swap the can for a 40/20/20/20. Suggestions?
Also, the amp is already fitted with an VVR currently scaling the whole amp. I could leave it as is or scale just the preamp (or remove it). How would the Mosfet react to the VVR?
Thanks!
Deric
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EZ81 will increase voltage X 1.3 similar to a GZ34. So, if your PT has 290v X 1.3 = 377v which would be fine for 6V6GT but not so great for EL84 or 6BM8 power tubes. .
I would VVR the power tube plates and screens and phase invertor and leave the V1 & V2a & mosfet alone. In other words, don't VVR the preamp but VVR the power amp. OR ................ remove the VVR and use a PPIMV to lower volume.
See the below schematic as an example. The schematic is another HoSo56 minimalist idea but has an active FX loop with it (which is an idea that I like. I have done an FX like this before with success). I have a layout for this idea also here:
http://el34world.com/Forum/index.php?topic=17863.0 (http://el34world.com/Forum/index.php?topic=17863.0)
IF you wanted to use 6BM8's, then I would recommend using a 5Y3GT, so IF your PT is 290v, then the volts to the plates would be close to 319v. Using the VVR to lower the plates further to around 300v or so would work really well, IMO.
With respect, Tubenit
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With the HoSo56 Minimalist from that other thread (that you linked to), you would VVR nodes A, B & C ......... but not D.
So, looking at the schematic with the VVR I posted in previous post, just eliminate node E.
How many preamp tubes do you have available to work with? What kind of power tubes are you thinking about using?
IF you can share a schematic of what you already have ............. it will be easier to help us answer your questions.
with respect, Tubenit
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I don't have a schematic. Was built from layout (attached) Brown Note posted several years ago called "Dirty 18". I mucked with it for a while but never ended up with something I liked.
Here's a pic of the amp. Currently running el84's but I'm fine with opening up the holes for 6v6. I do have a 5v tap for the rectifier so could change to other rectifiers If I need to drop some voltage...
https://goo.gl/photos/xv2eBASp2Rep2Wcz6 (https://goo.gl/photos/xv2eBASp2Rep2Wcz6)
The other amp I've been thinking about is a 6g2 and trying to squeeze in a SS reverb...
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Gee, you really did a nice job with the build! Very well done. Too bad it wasn't what you wanted.
Having said that, I got rid of every EL84 amp I've built or owned. They always ended up sounded too harsh and/or chimey to me. :dontknow:
I'm wondering if your current build would work for you if you simply changed to 6V6's?
Anyhow, I think the 6G2 would be nice .............. or you can try that HoSo56 minimalist with the mosfet CF and concertina phase invertor. Either would be the right tube number. IF you're using 6V6's, I think the EZ81 at around 377v would be fine. IF you want the 6G2 to have reverb, I would be inclined to maybe have a passive effects loop and run a reverb pedal thru the loop or simply thru the front end?
Leon C (forum member) built a 6G2 and I think it sounds really great:
! No longer available (http://www.youtube.com/watch?v=cnq_0b6WYjs#)
As a side note, I do like VVR's, but I've become more partial to PPIMV for a volume control. The VVR's have the advantage of lowering the voltage.
With respect, Tubenit