Tweedle Dee / mods or not?

[ChopSauce]

Thanks, Phil. I feel like a Tweedle Dee is more something of a sleeper, due to its Fenderish appearance & yet this build is definitely my own sauce, I think its circuit is more something of 55% Fender, 33% Dumble and 12% internet forum members ...

Anyway, I started wiring using https://www.stewmac.com/freeinfo/i-1073 ... ctions.pdf as a reference, together with pics of the real thing.
(note the board created from the pdf on the forum should ideally be a little shorter)

DSC08689.JPG

Now I guess I start to have an idea of what you guys can feel when completing the wiring of an amp such as an ODS, so far above the complexity of this one. This sure should be addictive...

However, the manual writes that the heater poles for the power tubes must not be inverted - that is the wire for pin #2 of V4 should go to pin #2 of V3, same for pins #7.

It was the first time I could read that...

EDIT: hosted picture on the forum

[ChopSauce]

Who said you can't fake patina?

Seems kind of truth to me: after hours of brushing/painting/sanding/dying/repeat, that one

DSC_6060b.jpg

came out. Some observations, from the first tests:

1. the amp was bassy enough for me so I decided to make both channels like the original Tweedle Dee Deluxe, rather than having one channel like the original 5E3

2. at VVR output the B+ seems to be spot on at (approx) 397V, yet the voltage is higer than 420V at VVR input (out of my memory) - using a GZ34 rectifier and TubeTown/inMADout 5E3 style PT

Now, the drawbacks:

1. yet the VVR allows for the amp to "crunch" at a lower volume, still it does not behave as a small power amp and I think I am going to also add a master volume - post PI, rather...

2. even at max VVR I have some scratchy (volume2) pot issue and measure some DC voltage at V2a grid. I swapped V1 and V2 coupling caps but this didn't changed much. Might that be the NFB cap?

When I'll have some time to investigate this latter issue I'll manage to replace the NFB cap, measure voltages and report.

Thanks for your consideration/support/help anyway,
___
(*) https://tubeamparchive.com/viewtopic.ph ... 14#p431514

[norburybrook]

when i put a VVR on my rocket I had to add an extra DC blocking cap to stop scratchy volume. I think if you google you'll see where that needs to go, or check my rocket/z wreck thread.


M

[ChopSauce]

Many thanks Marcus!

I think I could see xtian did that too. I've not seen your topic. I'll find it to have a look...

EDIT: found https://ampgarage.com/forum/viewtopic.php?t=29533
(installing VVR2 in rocket)

[fred.violleau]

Splendide!
Love that retro TV look!

PPMV, I would recommend LarMar type II, works great on my two builds.

Waiting for your clips now What speaker did you put into the combo?

Cheers!

Fred.

[ChopSauce]

Merci Fred !

Yeah, guess what: I'm just addicted to TV style fronts...

I put a Celestion Rocket 50 in it.

I'll have to sort the wiring a bit before playing it really. So far the amp is far too noisy. Unfortunately it will have to wait that winter comes and it's too cold to work outside.

[ChopSauce]

when i put a VVR on my rocket I had to add an extra DC blocking cap to stop scratchy volume. I think if you google you'll see where that needs to go, or check my rocket/z wreck thread.


M

I thought that you were talking about an additional reservoir cap but you were talking about blocking caps on the input, right?

I already have blocking caps on the inputs...

Some more head scratching hours to come to debug that issue...

[bepone]

really nice cabinet! Bartel style

[ChopSauce]

Latter... spouse told me she found the cab too mustardish/not brown enough, so...
(showing some "vintage-looking" post-processing filter for the picture)

DSC_6270-oldie.JPG

... & I am finally hitting some boundary with respect to noise reduction after having tested almost all the variations for the ground scheme & added coupling caps everywhere required by the VVR scaling the whole amp.

As obvious from the pic below - maybe - I must confess I took chances by using a switched pot for the VRR and the power on switch...

DSC_6271-oldie.JPG

Do you think I should be able to reduce the noise coming from the pot with a additional cap, which would provide an additional CRC filter together with the 10R resistor for the VVR?
(or maybe I should try another MOSFET than that IRF820?)

Thank you all for your support, anyway - and especially CW for additonal insights about grounding & lead dress(*). The outcome is already beyond expectations, yet not totally satisfying at full power, so far...
_

(*) https://tubeamparchive.com/viewtopic.php?f=4&t=34979

[fred.violleau]

Hey ChopSauce,

Nice update with the colour !
I have not played with VVR so I will not be of much help here... And I am sure you probably checked already power rating of the pot compared to what the VVR brings..

I was curious about this : "The outcome is already beyond expectations, yet not totally satisfying at full power, so far... ". What are you missing at full power, and when you say "full power" do you refer to the VVR full power? Or amp blasted loud ?

And yes even though rated a small amp, it does sound like a big amp !

Fred.

[bepone]

... & I am finally hitting some boundary with respect to noise reduction after having tested almost all the variations for the ground scheme & added coupling caps everywhere required by the VVR scaling the whole amp.

ma you have VVR close to network 230V ? it is very bad place for VVR, or any potentiometer actually.. and mosfet no need to mention how sensitive is this part.

pls remove VVR completely and make comparation of the noise VVR IN CIRCUIT/ VVR REMOVED it is the option to see what is a problem in your amp. yes yes is taking time, ofcourse. but you cant move forward if you dont invest your time

[ChopSauce]

Thanks for confirming my suspicions!

@Fred: I mean "amp blasted out" but it is obvious that the VVR pot is the most important "noise picker".

So yes, the VVR is in a bad place but it appears that it is always close to the voltage supply - on all the amps I could see - for it acts upon it, somewhat.

Do you think that some shielding may help?

You do need to mention how sensitive the MOSFET is because I have definitely no idea at all about that subject...

If everything else fails, I'll find a friend with another rectifier tube than the GZ34, because (I have none &) if the max voltage is spot on at the VVR out, it is (well) above 400V at its input so I wouldn't like to just take it appart, as is.

One update, though: it appears that I have at least one bad ground connection, so I can probably improve things.

[bepone]

i have fried hundreads of mosfets in mosfet HV regulator designs. mosfets are elements that are not plug and play, they are extremely fast devices and it is easy to destroy them. amateur installation will oscillate very easily (it can be out of the audible range but the oscillation artifacts can fall into the audible).
some guidelines for safe installation:
- one should take a mosfet that is designed for linear operation and not a switch mode (difficult but it is possible to find them)
- a gate stopper should be placed which is not a metal film (antenna) but non-inductive, carbon comp is a good choice, resistor very close to the gate
- an electrolytic capacitor that is not of large value (2.2uF-4., 7uF) that has not a small ESR (or install a 2 ohm resistor in series with the electrolytic cap) must be placed at the regulator output, because the charging currents during startup can fry the mosfet with low ESR or hi capacitance..

i was passing last years to IGBT elements, easy to drive them, and it is possible to find them in 1.3 kV + voltages , no any explosion in the last 5 years..

[ChopSauce]

Thanks for confirming my suspicions!

...

You do need to mention how sensitive the MOSFET is because I have definitely no idea at all about that subject...

I should have written "please, could you explain me how sensitive..." but you replied anyway so thank you twice...

Could you please mention a few MOSFET designed for linear operation, which - according to you - would be suited to the purpose?

Sorry, but my background is all about mechanics and metalworking, yet I can wire something as simple as a tweed Deluxe according to the schematic...

Also, need I understand that shielding the MOSFET (with something as a dog house) wouldn't help much - especially for I took care of routing the mains as far away from the MOSFET as possible...

[bepone]

ejla mosfets for linear operation are more expensive..
Here is one example IXTH12N100L (1000V, 12A, 400W part)

Mosfet what i'm using for DC regulator 400V is IRFPG50 (1000v, 6A, 190W part)

Every mosfet has one very sensitive input which dictates the behaviour, this is "g" input, gate, it is extremely sensitive. If you bring some noise to this input, this noise will be passed to the output. Noise can be any noise any frequency from low to MHz, and if the mosfet is ocillationg, then oscillations will be added to basic noise, so things easy can be worst than situation without mosfet.

If the voltage to the G pin is clean, then output will also be clean. So it is seen that is neccesary to clean very nice this voltage brought to the G input, means some filtering with R-C-R-C elements. I didnt see that in VVR designs around.
Also to make pin G less susceptible to external noise, no any wiring should be around this pin, and resistor soldered directly to the G pin leg, shuold be non-inductive (carbon composition 500-1000 ohms). If you put metal film there, metal film is antenna whis will collect external noise from area and will be inserted in the output over Gate pin!