imperial build questions

[geoff 1965]

i think that's pretty good for an initial fire up! what voltages do you have on the 6V6's?

[Bieworm]

I will drop that with 180+220R in series. And see where that puts it. The crunch is plenty imho, but the recording is through 2x10 sh*tty jensens. I might start tweaking when its in its 2x12 cab. There's a g12h30 and a classic lead waiting for it. But I'm doing the combo adjustments at the moment. I had to narrow it 1".
Thanks to you I did a success job. It's quiet, well laid out and I have done a lot of preparation this time. It's a hybrid deluxe reverb/tweed deluxe preamp with a cathode bias 2x EH 6V6GT poweramp. But it gives wayyyy more useable crunch than a tweed deluxe. The topology is 18W style.
Too bad for the turrets... my supplier of good turrets changed its supplier and now there were the crap unsolderable turrets delivered. Against good practice I ended up slightly drilling the inner holes to remove the coating and soldered all components in those holes. It went very well, but I'm aware this is not to your liking.. neither mine. But I discovered this when the turretboard was finished and it's like 90 turrets in there...
But I'm pretty happy with the result.. definitly because it worked just fine on the first flip of those switches 20201023_115631.jpg

Yeah, mediocre speakers would have that effect too. I look forward to hearing it with the right speakers/better bias.

It's all about prep work my friend. That's the key to success. You've certainly come a long way, and you're building some solid stuff now.

One trick you can also try with those turrets is to hit them with a wire brush, and then try pre-tinning them before installing anything.

Yet another lesson learned with the turrets... no more assumptions. Test befor the works..the FET tremolo works great too.. no thumping at all.
Have to change the volume pot on the clean channel. Because of the relays board I had to put in a 16mm pot and all I had was this dodgy 500k log. It doesn't operate as it should.

[Bieworm]

i think that's pretty good for an initial fire up! what voltages do you have on the 6V6's?

Think so too..

pin 8: 25V
pin 3: 429V
pin 4: 353V
cathode resistor 400R (bias 85%)
Cath bypass cap 22uf/100V (ain't that low?)

Also put in a 1/4 power switch. Nice for home playing

[JMPGuitars]

Think so too..

pin 8: 25V
pin 3: 429V
pin 4: 353V
cathode resistor 400R (bias 85%)
Cath bypass cap 22uf/100V (ain't that low?)

Also put in a 1/4 power switch. Nice for home playing

Much better dissipation! Post a new demo once you have the good speakers hooked up.

Your cathode voltage is 25V, don't you think 400% is a good enough safety margin?

[Bieworm]

99% finished.. a few hardware stuff and the reverb bag ( have to beg my wife to use her sewing machine )

20201025_144549.jpg

20201025_144542.jpg

[Bieworm]

Installed the corners and feet + added some trim between the faceplate and the grill. Very nice!!! Sad thing is I can't play it well since I cut the tip of my middlefinger off with an exacto yesterday evening ( slipped while removing excess tolex)

20201025_192439.jpg

16036505929212985579713808162742.jpg

[crgfrench]

I cut the tip of my middlefinger off with an exacto 20201025_192439.jpg16036505929212985579713808162742.jpg

Sorry to hear that! I did the same thing last year when I was changing the blade on a Zamboni at work. Fortunately it was on my right hand though.

[Bieworm]

I cut the tip of my middlefinger off with an exacto 20201025_192439.jpg16036505929212985579713808162742.jpg

Sorry to hear that! I did the same thing last year when I was changing the blade on a Zamboni at work. Fortunately it was on my right hand though.

Naah.. it will heal.. but stupid bad timing. But I play with what's left of my fingers hey
It sounds pretty neat! The OD has some of that swirl which we remove with the PR mod, but this thing has another PI so I'm not sure how to implement it... the 220k resistors don't go to ground, but to the oscilator (wiper of the int pot)

1603651164155635994417655263533.jpg

[JMPGuitars]

Naah.. it will heal.. but stupid bad timing. But I play with what's left of my fingers hey
It sounds pretty neat! The OD has some of that swirl which we remove with the PR mod, but this thing has another PI so I'm not sure how to implement it... the 220k resistors don't go to ground, but to the oscilator (wiper of the int pot)1603651164155635994417655263533.jpg

The PR mod is only for the EL84s. You could use a snubber (conjunctive filter) on your power tubes though, and see if that does the trick. You might also need to reduce the gain somewhere in the preamp.

Take a look at #4 on my EF86 Xtra schematic for the snubber: files/JMPGuitars_18_Watt_EF86_Xtra_Schematic.pdf

I think for two 6v6 power tubes you would change the 3K to 1.5K, and the .0047uF to .01uF.

I hope your hand heals quickly!

Thanks,
Josh

[Bieworm]

Naah.. it will heal.. but stupid bad timing. But I play with what's left of my fingers hey
It sounds pretty neat! The OD has some of that swirl which we remove with the PR mod, but this thing has another PI so I'm not sure how to implement it... the 220k resistors don't go to ground, but to the oscilator (wiper of the int pot)1603651164155635994417655263533.jpg

The PR mod is only for the EL84s. You could use a snubber (conjunctive filter) on your power tubes though, and see if that does the trick. You might also need to reduce the gain somewhere in the preamp.

Take a look at #4 on my EF86 Xtra schematic for the snubber: files/JMPGuitars_18_Watt_EF86_Xtra_Schematic.pdf

I think for two 6v6 power tubes you would change the 3K to 1.5K, and the .0047uF to .01uF.

I hope your hand heals quickly!

Thanks,
Josh

The schematic calls for a 1000pf 3kV snubber, but I broke its leg... maybe put in a new one...

[JMPGuitars]

The schematic calls for a 1000pf 3kV snubber, but I broke its leg... maybe put in a new one...

lol, probably. Be nice if it's that easy. Which schematic did you use?

[Bieworm]

The schematic calls for a 1000pf 3kV snubber, but I broke its leg... maybe put in a new one...

lol, probably. Be nice if it's that easy. Which schematic did you use?

The mk2 version I think.

20th_Imperial_SC200HB_pg1-1.pdf

20th_Imperial_SC200HB_pg2.pdf

[JMPGuitars]

The mk2 version I think.
20th_Imperial_SC200HB_pg1-1.pdf20th_Imperial_SC200HB_pg2.pdf

C44 is interesting. It's interesting to see the different variations on the snubber theme. I'd like to know if it's effective for you.

[Bieworm]

The mk2 version I think.
20th_Imperial_SC200HB_pg1-1.pdf20th_Imperial_SC200HB_pg2.pdf

C44 is interesting. It's interesting to see the different variations on the snubber theme. I'd like to know if it's effective for you.

Then let's find out .. I will stop by an electronics shop when I finish work.

[Bieworm]

The snubber is implemented.. the audible difference is not big, but it helps a little. It's not that same swirl on the decaying note we solve with the PR mod .. I think It's pretty normal with that enhanced mid bump the mid-bite pot creates. When I dial that back it disappears. I don't know yet if I don't like it.. I think I kinda do actually. Might be the honeymoon phase ...

I noticed something odd on the clean channel.. when I dime the bass it looses all bass. Beyond 3 O'clock it has no more bass. I already mentioned the volume pot is a 500k-A when it should be a 1M-A. Is there a link?

Another thing that puzzles me is that the wiper from the bass pot is connected to ground via a 10k resistor. Shouldn't the 3rd lug be that connection? On the DR it's the latter...