last little bit in 5F2A princeton with reverb and VVR

[phsyconoodler]

I'm coming up the home stretch in my newest build.A 5F2A with one tube reverb and VVR.
  I'm wondering if I should just scale the power amp and screen and leave the preamp at full voltage?I guess i could just try it and see what it sounds like with the whole amp scaled.The reverb would suffer at the lower voltages though.Hmmm....
Any thoughts?

[tubenit]

I would definitely opt for just the power amp & screen.

The reverb won't work if you get the voltages too low.

With respect, Tubenit

[Boots Deville]

yeah, I'll second what 'nit said.  I've put the VVR in a few SE's, and like it on the plate and screen only.

where did you insert the reverb?  In a BF Champ I used the 100K resistor between the reverb send/return as the grid stopper to the 6V6, so the 'verb returns right to the grid.  It works and I think it'll sound great once I find the right value for that resistor.  I think 100K is a little low.  I'm just curious where you spliced it in.

[phsyconoodler]

I haven't spliced it in yet,but that sounds like a good spot to do it.I'll try it and see what it sounds like.
  Thanks for the tips guys!
Why do you think it was a low value?Looking at the verb-0 champ layout in the sch files it is unclear about where I should mix it in in the 5F2A circuit.
  If you insert it right where the grid of the 6V6 is,it should work should it not?
Tubenit is definitely the one tube reverb master here.I still wrestle with where to mix it in in my builds.If it wasn't for tubenit,I'd be struggling along aimlessly.

[Boots Deville]

Why do you think it was a low value?

The reverb didn't have enough "presence".  To much dry signal compared to wet, so I need to tweak some values somewhere.  I've noticed that tubenit's schematics often show >100K values in that spot, so that's where I'll start.  This is my first implementation of the single tube reverb.

I tabled this build a couple months ago until I had a cab built for it and the speaker I wanted to use with it.  The cab is built - I just wrapped it in tolex yesterday, so it shouldn't be long now before I get to those reverb tweaks.

[jjasilli]

I think preamp voltages make a differnce re more headroom vs. early overdrive.  Maybe you could branch off the reverb B+, and VVR the preamp; or use a SW to drop voltage to the preamp.  EDIT:  OTOH, a hi voltage preamp can be made to overdrive with a raw control. - whoops wrong tonestack  Just some ideas.

[phsyconoodler]

I've decided just to regulate the plate and screen.However,it is still unclear to me where to mix the reverb in the 5F2A circuit.The blackface champ in the archives has an extra tube and it's unclear where I should mix it in.

[Boots Deville]

Not sure what you mean by the extra tube, but I've attached a schematic showing how I did it.

[phsyconoodler]

Thanks Boots,
  In the archive it shows an extra tube in the schematic.Some hybrid champ layout.Nothing on just the champ.

[tubenit]

Physconoodler,

I have NOT built a Champ with reverb, so I can't offer a "proven" model of my own. 

In the SCH Library there is a 5F2 with reverb built by Chrisrbr:

http://www.el34world.com/Forum/index.php?topic=630.0

However, he used the traditional Fender reverb. I took his schematic and changed it to a one tube reverb that might work?  You'll have to experiment with it.

With respect, Tubenit

[Fresh_Start]

I haven't done this, but might there be an advantage to inserting the reverb right after the Volume pot & before the second gain stage?  Might give you more flexibility in terms of the wet/dry mix, especially if you tweak the gain of that second triode a bit.  Also, it would leave the 6V6 with "vintage" values for it's grid return resistor.

Just wondering out loud,

Chip

[phsyconoodler]

The extra tubes are throwing me.The mix point is still not clear.I'm going with Boots' layout.
  It may work fine,I'll find out later this week.
I've done the 5F2A two tube reverb before but it didn't work that well.It squealed when the reverb was turned up too high and nothing I did helped that.
  We'll see.

[jjasilli]

I'm going with Boots' layout.  Agreed.  But note that if you VVR the power tube, won't that will vvr the reverb driver also?

[tubenit]

I think Boots schematic is definitely worth trying. Just hook up the reverb trannie to node C instead of B as jjasilli pointed out when using the VVR.

Please let us know how it works out. I am very curious about this one.  Remember if you need more verb switch the 1M pot out for a 2.2M pot.

With respect, Tubenit

[phsyconoodler]

Yeah I'm not sure what will happen.I'm going to try just the power amp and see what it sounds like.The reverb should get much more presence as the VVR gets turned down.Similar to the D'lite when the master goes up,there is more reverb.Turning up the volume in the 5F2A will give more reverb and turning the VVR down should increase the effect.

  I may fire it up tonight.I'm already using a 2meg pot.
Thanks for all the input!

[phsyconoodler]

Well the amp is up and running but the reverb is not working.I have a couple of questions about the mix point.
  1) inserting it in the grid line to the powertube doesn't seem to work at all.It's really not a difficult circuit so I don't have it wired wrong
  2) when adding the cathode R/C's is it necessary to have one for each cathode or can you combine them?(reverb tube)
  3) I can get the tank to splash a bit but it just oscillates when turning the reverb control up.

 On a plus note,the VVR works flawlessly and retains the highs quite well even though I scaled the whole amp,not just the plate and screen.
This amp is dead quiet at idle,which is a first for my single ended experience.I used an extra filter cap for the VVR which may be why.The tone of the amp overall is really nice,with a nice Champ style breakup.I'm using an NOS 5Y3 and RCA 6V6 with a Philips ECC83.

[jjasilli]

We know the power amp works.  Work backwards from there into the reverb circuit.  With the amp on, touch a volt meter probe to the plate of the reverb recovery tube.  You should get a pop in the speaker. Then then touch the grid of that tube.  You should get a louder pop (due to the tube's amplification).  Then do the same with the reverb driver section.  If at any point you don't get a pop, then signal is not making it past that point.  So, the problem is there, or somewhere before that point. 

(For a reference touch the meter probe to the plate and grid of the tone recovery stage. That's what the pops should sound like.)

[phsyconoodler]

Ok,here's an update on the amp.
  The reverb works now,but it will not work with a 100k mix resistor.I upped it to 560k and there is reverb but it's not a good sounding reverb.
   The amp doesn't like it much because it distorts the signal too much.
There must be a better place to mix the reverb into this amp.The driveline seems to a bad place because it affects the 6V6 too much to have a large grid resistance like that.
  any other place a guy could mix the reverb in and not affect the grid?

[Boots Deville]

Do you have Merlin's book?  If so, check the effects loop section - he shows some examples of where to take the signal from, and where to return it to that might give you some ideas.

I know you said it didn't work at all for you when mixing it at the 6V6 grid.  Did you retry it there after you got it working elsewhere?  It works for me.  I still need to tweak with it before I can call it a "done deal".

[phsyconoodler]

I'm still mixing it there,but as you increase the mix resistor value,the tone suffers greatly.The amp distorts way too early with a large grid resistor in there,but without it there is almost no reverb.
 The insertion point is the key.

[Fresh_Start]

I know Boots has success with his circuit, but at the risk of being an ass, did you consider this possibility?  

I haven't done this, but might there be an advantage to inserting the reverb right after the Volume pot & before the second gain stage?  Might give you more flexibility in terms of the wet/dry mix, especially if you tweak the gain of that second triode a bit.  Also, it would leave the 6V6 with "vintage" values for it's grid return resistor.

Just wondering out loud,

Chip

You might even try putting the insertion point between the tone stack and the volume pot.  That would give you a constant, and higher, signal level going into the reverb driver.  IIRC when Fender re-worked their Blues Jr. they moved the reverb takeoff/insertion point from after the volume pot to before and it supposedly reduced reverb noise levels when the volume is turned down. Wrong tone stack!

I couldn't figure out how to copy & paste the 1-tube reverb into my 5F2-A schematic, but the attached file shows an alternative.  I'm pretty sure you'd need to do something to boost the gain of the second triode to make up for signal loss caused by inserting the reverb (two 1-meg resistors in parallel with the Volume pot to start with).  220K plate resistor would be my first choice, but I kind of like that tone anyway.

Hope this helps,

Chip

[tubenit]

You might even try putting the insertion point between the tone stack and the volume pot

On the original Carolina Blues Special amp I built, I placed the insertion point around the volume pot between the 1st and 2nd preamp gain stages. It worked fine. However, it was slightly interactive with the volume.

With respect, Tubenit

[phsyconoodler]

Hey tubenit,
  Do you have the link to that schematic?

[tubenit]

Here is the schematic.  I built about 4 or 5 amps using this type of insertion point and all of them worked OK .......... but it is interactive with the volume knob somewhat.

With respect, Tubenit

You can also look at the Gibson Scout GA-17RVT

[phsyconoodler]

You're the best Tubenit!
  While I was pondering,I actually put the 100k mix resistor in line with the wiper of the volume control and simply mixed the reverb there with no other changes and it works great.Lots of reverb,but it does affect the quality of the tone a bit.A little tweaking and I should be there.Now the mix resistor size will be the key.Have to find my Heathkit resistor substitution box and get to work.

So basically all I did was insert a 100k resistor in series with the wiper and inserted the reverb right there.It's not very reactive with the volume;it seems to have lots of reverb even with the volume rather low.Hmm.....

[Boots Deville]

phsyconoodler, in that case, I'd disregard my experience, because you've gotten to where I'm at, and gone beyond with your tweaking.  It's very possible I'll come to the same conclusions as you have when I get back to it.  I'll be following this with interest! 

[tubenit]

all I did was insert a 100k resistor in series with the wiper and inserted the reverb right there

Great to hear you got it working!  The reason the way I did it was somewhat interactive was I was "cheating" and actually using the volume pot itself like a mixing resistor. So when the volume pot was changed, it changed the size of the mixing resistor ........... sort of.
 

With respect, Tubenit

[phsyconoodler]

It seems to work very well where I have it now.Unfortunately I'm playing it through a crappy mesa cab with a very,very bright Eminence speaker that sounds pretty hideous.I'll try it through a different cab and report back.
  But overall the reverb tone is great.
Now to figure out what the VVR stopped working......
  This week has been nuts!
You guys are the best however.I wish we could all get together for beers and jam our asses off!

[phsyconoodler]

So we use Boot's schematic and simply put the mix resistor in series with the volume wiper.I didn't change anything else.So far so good.
Again,you guys are the best!You make me think,it keeps me young.That and playing blues at jams.

[Fresh_Start]

So we use Boot's schematic and simply put the mix resistor in series with the volume wiper.I didn't change anything else.So far so good.
Again,you guys are the best!You make me think,it keeps me young.That and playing blues at jams.

I'm confused (or slow this afternoon).  Are you inserting the reverb right before the grid of the second triode gain stage?

BTW my suggestion to put the insertion point between the first triode and the volume/tone pots was based in part on trying to avoid (1) interaction with the volume pot and (2) having too much reverb at lower volume levels.

Cheers,

Chip

P.S.  I'd take you up on the beer suggestion any time!          :drunken_smilie:

[phsyconoodler]

The center lug(wiper) of the volume pot to the grid(pin 7) of the second triode is where I put the 100k mix resistor.Then I simply added the other wires.One from the reverb pot and the other from the reverb send(pin 2 on the reverb tube)
  It works great and there is not too much reverb at low volume levels at all.
The amp sounds great and the reverb sounds much better than mixing it at the 6V6 grid.MUCH better.

[Boots Deville]

Does the attached schematic accurately reflect what you did?  

I put a 5K6 on the 6V6 grid in the schematic, but the AA764 champ had no grid stopper.

Edit: I've updated the attached schematic per phsyconoodler's comments below.  I've removed the 6V6 grid stopper and the 1K/5W screen resistor.

[phsyconoodler]

Yes that's correct.But,get that grid stopper out of there!It alters the tone,and not in a good way at all.They don't need it at all.
  I don't use screen resistors either.The amp simply doesn't need them.I do however,up the cathode resistor to 560 ohm from the stock 470 ohm.The plate dissipation is rather high at 470 ohms.
  You will love the reverb and the way the amp sounds.

P.S. got the VVR working.Just a bad connection.It works flawlessly.As expected,the reverb drops out at the lowest settings,but I don't care about that.

[tubenit]

Thanks for sharing your hard work and success on this!  I'll put a SCH version of this into the SCH library.

http://www.el34world.com/Forum/index.php?topic=630.0

With respect, Tubenit

[Fresh_Start]

Physconoodler - Thanks for sharing your development work with us!

Did you build your amp with the Blackface Champ TMB tonestack or the Tweed Princeton tone control?  Looks like TMB from all of the schematics but the thread title says "5F2-A".

Only because I'm extra cost conscious due to ordering parts for a new build right now, Hammond's 155H choke (5 Henries @50ma) costs a buck or two less than the 194H (4 Henries @50ma).  They appear to be the same size physically.

Cheers,

Chip

[phsyconoodler]

Mine is totally a Tweed 5F2A with just a tone control.
  I put it in it's cabinet last night and the sound is, wow!
 The reverb works great and the amp sounds wonderful.
   I'm using the Eminence speaker that comes in the Hot Rod Deluxe amps.It sounds much better than I would have imagined.

 A double round of applause for Boots,Tubenit and everyone else who shares their skills freely with this forum.!!

[echuta13]

I was planning on building a 5f2a'ish amp with reverb @ some point, and was concerned about how I could intergrate the reverb in.  This will give me a great starting point if/when I get around to it!  Thanks guys.   

[phsyconoodler]

It works very well.I am very happy with the results.