V2a
Active member
criss-cross apple sauce
FourT6and2
Well-known member
I'm guessing you had a bad joint somewhere. And when you swapped the grid/cathode connections, it fixed the bad joint.
SpiderWars
Well-known member
You're correct it's for taming oscillation. You usually don't really need it. How does it sound?
ledvedder
Well-known member
It sounds really good so far. A little loose and boomy in the lows, but that seems normal with this circuit. I suppose that's why so many push it with an SD-1 or similar. And it seems a lot of people drop the caps down to 0.0022uF.
ledvedder
Well-known member
I also think my voltages at the PI going forward might be a bit low. I swapped the 10k before the PI to 20k. That brought it down to 312v. I think it's best somewhere in the 330-360v range.
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burger
Well-known member
320 to 330 for a 2204 is your target
ledvedder
Well-known member
Maybe an 18k instead of 20k?
glpg80
Well-known member
Congrats on getting it sorted out!! It’s a great feeling for sure.
Now that you’ve got it working as a true 2204 and know what it sounds like, what’s the plan?
Now that you’ve got it working as a true 2204 and know what it sounds like, what’s the plan?
ledvedder
Well-known member
Thanks for all your help!
I thought about the 34 mod, but so many people say it's really harsh.
I'm thinking I wanna make the JEL spec switchable. Maybe a switchable 3k3/0.68 across the 10k. A 0.0022uF switchable in series with the 0.022uF. And a switchable 22uF across the 820r.
Basically Headfirst's (@burger) mod.
ledvedder
Well-known member
I also have an effects loop from Headfirst that I'm gonna put in it.
And I'll probably elevate the heaters. 470k/82k off of the 441v screen supply should give me about 65v.
And I'll probably elevate the heaters. 470k/82k off of the 441v screen supply should give me about 65v.
glpg80
Well-known member
From experience I’d solder the cap permanently across the 820. The added gain boost is nice and IMO it just sounds better.
Bump the 0.0022 up to 0.0033 to keep the amp from thinning out.
I’m not a fan of messing with the 10k cold clipper. I always feel messing with that stage always sounds better stock as is, but that’s me.
The loop is a good addition. Don’t make the same mistake I did and install it after the master. My 74 is like that right now and eventually I need to move it to before the master so that low volume playing tone doesn’t take a crap.
When you elevate the heaters using the center tap be sure to solder it well. 65V DC cold solder joints on the heaters will pop really, really loud.
ledvedder
Well-known member
If I do the 0.0022 cap, I'll probably add a depth circuit to the NFB.
Or who knows... Maybe I'll play it for a bit and decide I don't want to change anything.
Or who knows... Maybe I'll play it for a bit and decide I don't want to change anything.
burger
Well-known member
If you thin out the bass in the pre, you really need to bring it back in with a depth circuit.
The loop will drop the PI supply voltage a bit, so fine tune the dropper after the screens once you have the loop in place.
The loop will drop the PI supply voltage a bit, so fine tune the dropper after the screens once you have the loop in place.
glpg80
Well-known member
That doesn’t make a lot of sense to me? A depth circuit is within the negative feedback path. Can’t add back in what isn’t there. The pole for 0.0033 is still very much well within guitar frequency range so there’s no concern for blocking distortion going smaller. I’d argue instead with the stock value 0.02uF will be of concern especially as gain is increased. A depth circuit would be most beneficial to add the punch factor by removing bass with the stock value.
SpiderWars
Well-known member
But isn't the NFB taking something out and the Depth circuit is just preventing that from happening in the lows. So the lows were there in the first place and the NFB is removing them (actually NFB reducing gain in general but then we sculpt out the highs/lows with Presence/Depth).
mcstinger
Well-known member
@glpg80 I think it makes a sense. You attenuate bass frequencies (they are still there) before distortion stage(s) and then you pull them up again. 5150 III i.e.
glpg80
Well-known member
NFB is a series resonance so it goes open circuit at resonance taking away NFB which allows bass from the preamp to go to the speakers without phase cancellation.
SpiderWars
Well-known member
@burger I've seen your JEL mod video and it didn't appear you had any issues with it being too bright? But digging into the Friedman JEL, it seems many/most people that have actually played it say that the JEL mode is really, really bright. Almost like they didn't want to come out and say it's too bright. Even Dave says this. Which is what I experienced when I did mine, I had to add a snubber to the Gain control bypass resistor.
ledvedder
Well-known member
Or maybe I'll do a 3 way switch to get both the JEL and a #34 thing? 3k3/0.68 on one side, and 0.01 on the other side. Stock 10k in the middle. 
SpiderWars
Well-known member
I do agree with @glpg80 that the 10k has something different/unique about it that it's nice to have the option. That plus an SD1 up front is still tough to beat. Just note that on the JEL there is another resistor to ground that is switched in simultaneously, so you're increasing gain in one spot but reducing it in another. That resistor can be adjusted but I think its 220k in the JEL. It would probably be a fuzzy mess without that resistor.Or maybe I'll do a 3 way switch to get both the JEL and a #34 thing? 3k3/0.68 on one side, and 0.01 on the other side. Stock 10k in the middle.