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Re: imperial build questions

Posted: Fri 10/23/20 8:53 am
by geoff 1965
i think that's pretty good for an initial fire up! what voltages do you have on the 6V6's?

Re: imperial build questions

Posted: Fri 10/23/20 9:01 am
by Bieworm
JMPGuitars wrote:
Fri 10/23/20 8:46 am
Bieworm wrote:
Fri 10/23/20 8:11 am
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.

Re: imperial build questions

Posted: Fri 10/23/20 9:25 am
by Bieworm
geoff 1965 wrote:
Fri 10/23/20 8:53 am
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

Re: imperial build questions

Posted: Fri 10/23/20 1:59 pm
by JMPGuitars
Bieworm wrote:
Fri 10/23/20 9:25 am
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? ;)

Re: imperial build questions

Posted: Sun 10/25/20 9:12 am
by 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

Re: imperial build questions

Posted: Sun 10/25/20 1:30 pm
by 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

Re: imperial build questions

Posted: Sun 10/25/20 1:35 pm
by crgfrench
Bieworm wrote:
Sun 10/25/20 1:30 pm
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.

Re: imperial build questions

Posted: Sun 10/25/20 1:41 pm
by Bieworm
crgfrench wrote:
Sun 10/25/20 1:35 pm
Bieworm wrote:
Sun 10/25/20 1:30 pm
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

Re: imperial build questions

Posted: Sun 10/25/20 2:17 pm
by JMPGuitars
Bieworm wrote:
Sun 10/25/20 1:41 pm
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

Re: imperial build questions

Posted: Sun 10/25/20 2:22 pm
by Bieworm
JMPGuitars wrote:
Sun 10/25/20 2:17 pm
Bieworm wrote:
Sun 10/25/20 1:41 pm
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...

Re: imperial build questions

Posted: Sun 10/25/20 3:25 pm
by JMPGuitars
Bieworm wrote:
Sun 10/25/20 2:22 pm
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?

Re: imperial build questions

Posted: Sun 10/25/20 3:49 pm
by Bieworm
JMPGuitars wrote:
Sun 10/25/20 3:25 pm
Bieworm wrote:
Sun 10/25/20 2:22 pm
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

Re: imperial build questions

Posted: Sun 10/25/20 6:49 pm
by JMPGuitars
Bieworm wrote:
Sun 10/25/20 3:49 pm
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.

Re: imperial build questions

Posted: Sun 10/25/20 10:32 pm
by Bieworm
JMPGuitars wrote:
Sun 10/25/20 6:49 pm
Bieworm wrote:
Sun 10/25/20 3:49 pm
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.

Re: imperial build questions

Posted: Mon 10/26/20 1:34 pm
by 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...

Re: imperial build questions

Posted: Mon 10/26/20 2:35 pm
by Bieworm
Bieworm wrote:
Mon 10/26/20 1:34 pm
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...
Edit: after looking at online pics of the imperial I noticed the bass pot is wired backwards on the schematic. So I have to move the wire from lug 1 to lug 3. Going to do that later this week when my 500V filter caps arrive, along with the 1M vol pot and the 1M-RA speed pot.

Edit #2: swapped the wire and now it works normal. Djeez a log pot is unrecognizeable when wired incorrect. The taper is so misleading...

Re: imperial build questions

Posted: Tue 10/27/20 6:34 am
by Bieworm
Screenshot_20201027-123515_CamScanner.jpg
another thing I think is incorrect about the imperial schematic. It connects the screen grid to B3, which is only about 350V. It think it'd be better to downsize the resistor between B2 and B3 so I can raise that to 410V. Maybe I should try swapping R87 en R88's values so there is 5k between B2 and B3 / 10k between B3 and B4. That seems to make more sense to me.
Sad thing is I don't have any reference voltages for the imperial besides the 5E3 and BFDR voltages. the schematics of these are pretty similar to the imperial preamps. The PI is very different.
It would also make more sense to have a higher voltage on B3 for the reverb because the BF reverb has also got 410V on the plates of the send half and 170V on the platse of the recovery half.

anyway, the difference of +-80V between plate and screen on those 6V6's don't seem right...
and I think I will also try out what the effect of a bypass cap on the cathode from V1 will bring. There is none on the schematic, but maybe it's better with one? Both the 5E3 and the BFDR have one. OTOH it might be overkill for the OD channel, which shares that first preamp stage...

Re: imperial build questions

Posted: Tue 10/27/20 9:10 am
by JMPGuitars
Bieworm wrote:
Tue 10/27/20 6:34 am
anyway, the difference of +-80V between plate and screen on those 6V6's don't seem right...
Did you arbitrarily decide that, or did you do research first?

What do we know about the relationship between screen and plate voltages?

What about safe voltage limits for the screens on 6v6 tubes?

Have you looked at datasheets comparing the voltage differences, especially in higher voltages such as you're using?

Re: imperial build questions

Posted: Tue 10/27/20 9:37 am
by Bieworm
JMPGuitars wrote:
Tue 10/27/20 9:10 am
Bieworm wrote:
Tue 10/27/20 6:34 am
anyway, the difference of +-80V between plate and screen on those 6V6's don't seem right...
Did you arbitrarily decide that, or did you do research first?

What do we know about the relationship between screen and plate voltages?

What about safe voltage limits for the screens on 6v6 tubes?

Have you looked at datasheets comparing the voltage differences, especially in higher voltages such as you're using?
Not much. Just thoughts on comparison with similar amps. It's all hypothesis... not planning anything yet. The amp sounds fine as is.. going to play it for a few weeks. Maybe it's the fear of falling into the void concerning building stuff. But hey, there's still that reverb for the tremolo TMB lurking 😄

Re: imperial build questions

Posted: Wed 10/28/20 3:15 pm
by Bieworm
Compared the OD of the imperial with the tremolo TMB. Man that's no contest at all. The TMB is far superior.
A hypothesis... the imperial is dual channel the TMB single. Suppose I remove the components from the lead channel of the imperial and implement the components of the TMB. Adjust the voltages to the TMB voltages ofcourse. Would I be able to have the drive channel of the tremolo TMB along the clean channel of the imperial?
Important note is that I never push the power tubes into OD on my TMB , so I conclude it's the preamp OD I love so much.
The mid pot circuit can be easily mimic'd with fixed resistors, no? I always turn it to near max, so I make the compromise of not being able to tweak that anymore.
Is there some logic in this hypothesis? Am I overlooking some crucial things?
Ofcourse I will have to move stuff around to maintain the clean channel. + the imperial shares the 1st preamp triode for Josh channels, so I am aware of the possibility the voltages from imperial to tremolo TMB 1st preamp stage will have an impact on the clean channel too. Although the voltages don't differ that much...