imperial build questions
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Re: imperial build questions
i think that's pretty good for an initial fire up! what voltages do you have on the 6V6's?
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Re: imperial build questions
Yet another lesson learned with the turrets... no more assumptions. Test befor the works..the FET tremolo works great too.. no thumping at all.JMPGuitars wrote: ↑Fri 10/23/20 8:46 amYeah, mediocre speakers would have that effect too. I look forward to hearing it with the right speakers/better bias.Bieworm wrote: ↑Fri 10/23/20 8:11 amI 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
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.
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.
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Re: imperial build questions
Think so too..geoff 1965 wrote: ↑Fri 10/23/20 8:53 ami think that's pretty good for an initial fire up! what voltages do you have on the 6V6's?
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
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Re: imperial build questions
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?
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Re: imperial build questions
99% finished.. a few hardware stuff and the reverb bag ( have to beg my wife to use her sewing machine )
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Re: imperial build questions
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)
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Re: imperial build questions
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.
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Re: imperial build questions
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)
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Re: imperial build questions
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.Bieworm wrote: ↑Sun 10/25/20 1:41 pmNaah.. 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
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
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Re: imperial build questions
The schematic calls for a 1000pf 3kV snubber, but I broke its leg... maybe put in a new one...JMPGuitars wrote: ↑Sun 10/25/20 2:17 pmThe 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.Bieworm wrote: ↑Sun 10/25/20 1:41 pmNaah.. 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
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
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Re: imperial build questions
lol, probably. Be nice if it's that easy. Which schematic did you use?
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Re: imperial build questions
The mk2 version I think.JMPGuitars wrote: ↑Sun 10/25/20 3:25 pmlol, probably. Be nice if it's that easy. Which schematic did you use?
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Re: imperial build questions
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.
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Re: imperial build questions
Then let's find out .. I will stop by an electronics shop when I finish work.JMPGuitars wrote: ↑Sun 10/25/20 6:49 pmC44 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.
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Re: imperial build questions
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...
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...
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Re: imperial build questions
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.Bieworm wrote: ↑Mon 10/26/20 1:34 pmThe 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 #2: swapped the wire and now it works normal. Djeez a log pot is unrecognizeable when wired incorrect. The taper is so misleading...
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Re: imperial build questions
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...
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Re: imperial build questions
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?
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Re: imperial build questions
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 lurkingJMPGuitars wrote: ↑Tue 10/27/20 9:10 amDid 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?
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Re: imperial build questions
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...
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...
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