new tweed voicing

[afm_380]

My first build was a 5e3 clone, which came out amazingly well. And I've had a blast re-voicing the two inputs slightly by splitting the shared cathode bias and playing with different cap and resistor values. The two inputs are still too similar (and I haven't tried any vox likes yet ...). So here's my plan ...

Add another preamp tube for an additional gain section to one input stage, and a cathode follower driver for an FMV tone stack. I'd also like to run EL34's in the power stage ... so I've added another small transformer to power the preamp tubes. It's 12.6v/2a, so I either run the preamp tubes at 12.6vac, or build a rectifier bridge and power the three tubes in series on dc. Here's the schmatic of my mods ... I still need to validate what coupling caps I will be using, obviously the .1's will need to be trimmed down to probably .022's (but I already have a nice supply of .047, .033, and .022 ... ;o).
The B+ voltages are what I'm currently getting with the 5y3 in place with 6v6's, I'll more than likey run the EL34's with an ss plug (or a gz34).

Have I missed anthing ???

Merlin's book and this forum have been a tremendous help in feeding my new found obsession of building and tweeking tube amps ... Thank You All

[axpro]

Looks interesting...

ONly concerns I can think of is that with the extra gain stage on the vox side, the signal would be inverse to your fender type signal, so you couldn't bridge them.

And in the circuit, you are running a signal from v2b (between ra13&14) tot he cathode of the cathode follower stage? I am unfamiliar with that circuit.


Let me know how it sounds though, si nce i am hating my 5e3x2, even though it is a proluxe with a 6g2 type pre this week.

Maybe i'll just make it a tiny little JCM800!

[afm_380]

Thanks axpro ...

I haven't bridged the inputs (but I understand that it's a common practice in the 5e3 world) so it's really not any issue that I'm too concerned with. I'll more than likely build it as I have drawn to see how it preforms with the next revision adding yet one more preamp tube with one stage used to synchronize the stage inversions and possibly the second stage being used to change the phase invertor to an LTPI ... another possibilty would be to add an opamp into the circuit simply to sychronize the stage inversions (blasphemy ... ;o).

The unfamiliar circuit is taken from pg131 of Merlin's book ... it's a technique used to "bootstrap the previous stage's anode resistor to increase gain". I'll probably also add a switch to lift this out of the circuit.

What part of the 6g2 pre are you using (to me it looks like a single channel 5e3 with tremolo and negative feedback)? Did you add NFB?

[axpro]

Sorry AFM, i meant to say 6G3... changes the layout of the volume controls and adds mixing resistors. makes them much less interactive. The version i see of this uses a dual pot for tone (so it affects both channels) but i didn't have one, so one channel has a tone control and the other is "au natural" Works well with pedals.

I did add a negative Feedback.

The amp is ok, but i am not loving it. I think when i am done my current project (Princeton High Power kit), I am going to rebuild it yet again into something DRZ-ish, with an EF86 and maybe a pair of el34's. I used to LOVE my Z28 head, and I figure its a simple enough circuit that i can put it in this shell and not constantly fight for space.

[pdf64]

A couple of things with the schematic are
1 no dc blocking cap between V2a and the mixer resistors.
1a those mixer resistors are a bit small at 100k, 270k or 470k would give better isolation.
2 the lower turnover frequency of each stage is very low, running the risk of flubbiness and blocking distortion
3 given the above, the power supply de-coupling might be inadequate, resulting in motorboating at high gain/bass/vol settings.

A fix for 2 might also fix 3.
I'm planning on trying out Merlin's CF bootstrapping trick soon also.

[afm_380]

Thanks pdf64 ... now I get to research the possible fixes for issues 2 and 3 ... fortunately I understand issues 1 and 1a.

[afm_380]

it's built ... now the fun REALLY begins ... ;o)

a status update ... to address the issues that pdf64 brought to my attention,
1 - I added a .033uF cap between V2a and the mixing resistors (Rg12)

1a - I had to increase RG12 mixing resistor to 1M to isolate to Vox channel
from drawing the Tweed channel to a whisper

2 and 3 - not sure I addressed these correctly, but I changed the values of
the coupling caps to C1=.047uf, C4=.033uf, C12/C13=.022uF

Merlin's CF bootstrap trick is pretty sweet ... It definitely adds some nice smooth grit really early ... maybe too early on the tweed channel. A switch will need to be added until I decide whether to keep it or not.

I'll probably bring it out to an open jam tonite to see how well it's accepted.

I just came across this schematic for the TopHat King Royale. It looks REALLY close to what I was tying to attempt. If I can't get this current build tweeked just right, I may fall back to rebuilding it once again ... ;o)

Thanks again for all of your help and comments.

[afm_380]

WELL ... I've spent a couple of day changing things around in an attempt to find a better balance between to two channels (I need to keep better notes of my changes along with the results .. starting to get a little lost as to 'what's doing what'). One VERY interesting finding is that if I lift the ground on the Master Volume the tweed channel comes alive (the master volume no longer acts as a master volume obviously ... ;o). Now I just need to come up with a way to lift this ground when the cable is plugged into this channel (but this scheme defeats the goal of being able to use an A/B box to provide channel switching ... maybe I need to re-think this build).

I think I'll add a couple switches (one to lift the MV ground, and one for Merlins CF Bootstrap) and play it a while before I pull everything out and wire it up as a KR clone.

[Bruce / Mission Amps]

I've never done this without a blocking cap on the wiper of the MV pot to the grid of the PI triode.... but your MV pot is DC grounding your fixed bias phase inverter.... is that the way you were told to do it?
Think about what happens to the voltage divider with the pot set to zero....
I don't know if that would hurt anything or not but, I'd lift the grounded lug of the MV pot and use a .1uF 400v cap to ground myself and see what happens.

[afm_380]

It's time for an updated schematic ... Here's how it's currently built. I needed to add a blocking cap between the wiper of the MV and the grid of the PI to quiet the pot down (I can probably remove the original cap ... but it doesn't appear to be causing any adverse effects ... I ran a jumper across it and couldn't tell any difference). I'll add the .1uF as suggested.

This is my own rendition of attempting to morph one channel of a 5e3 with a voxish voicing. It's been an interesting ride ... ;o)

[Bruce / Mission Amps]

It's time for an updated schematic ... Here's how it's currently built. I needed to add a blocking cap between the wiper of the MV and the grid of the PI to quiet the pot down (I can probably remove the original cap ... but it doesn't appear to be causing any adverse effects ... I ran a jumper across it and couldn't tell any difference). I'll add the .1uF as suggested.

This is my own rendition of attempting to morph one channel of a 5e3 with a voxish voicing. It's been an interesting ride ... ;o)

You don't need Cg9 now but use a bigger cap on the bottom of the MV if you do that way... so it doesn't act like a tone control.
I looked at my notes and I actually used a .47uF cap on the bottom of the MV pot... sorry.

[afm_380]

OK ... The MV now goes to ground via a .68uF wima. No noticable difference here at the house. It's time to button it up and play on it a while. I'll try to take it out to an open jam tomorrow evening, and put some other players thru it. It should be fun anyway ... ;o)