Advice on sort of El84 Princeton reverb w/o tremolo or similar circuit help

[Jerry garrcia]

Hi all. I’ve got this dumb Filmosound amp. Originally running on 2x2 UL84’s and a “transformer” mounted on the cabinet for optional input voltages.
A not very stout construction of the chassis and the upper part is a mess, and so is the rest of the amp in my opinion. Thin PCB design and as always in Filmosounds everything is cramped together.
So I was planning on ripping it all out and use a separate chassis for the power supply, cut a fresh plate of aluminum to use as the top plate and mount in the chassis.
I’ve got to many strange and labor intensive projects now so am looking to do an easy board build with noval socket tubes (or 7-pin if needed). Have two PT’s spare. No 5V windings and one 190-0-190V and the other 250-250V without a CT.
initially I was thinking of a AA1164 without trem/reverb with el90’s but my son just said that his reverb pedal was gone.
So have to have a reverb. Since I really like the faceplate with “volume”, “treble” and “bass” I don’t want to add more than one pot so I’m thinking of skipping the dwell pot and replacing it with a resistor.
Have some 12ax7’s, 12at7’s, el 90, el95’s and el84’s. A nice 8K pp OT.
So was looking att the Hoffman's Stout with reverb but would rather have a classic T(M)B tone stack.
Should I go with that circuit or does anyone has any other suggestions?
So preferably a board mounted circuit and since he wants it for a gig in two weeks if anyone has a layout 
Also got some ef86 in a drawer somewhere.
It will be safely mounted in a 12” bell & Howell speaker cabinet where I will cut a hole in the front to access the front panel.
I usually go with “different” circuits that takes a lot of tinkering and troubleshooting but here I just want to make it quick easy. But good sounding of course. Cathode or fixed bias doesn’t matter.

[Jerry garrcia]

Just a clarification. Not really voiced as a marshall but more like a fender or old school Gibson. Listen on YouTube at Hoffman 18W stout and found that a bit to “British/ harsh” sounding.
I’ve done a Princeton Reverb for a friend and I really like it and a couple of 5C1, 5B2’s, pp tweeds, EH-185, GA20’s sort of. So more voiced American, if one could say that?
I usually build out of known schematics with tweaks that I get helped with but now due to time issues I’m gladly willing to do a clone/copy. Mostly for jazz, some lowfi rock, grunge, Roky Erickson. The reverberation just for getting a fuller sound for gigs. So no need of a surfy reverb.

[bmccowan]

I see another Filmosound in the background, so you likely know what a pain in the ass this will be. Its a lot of work to do because you like the faceplate.
Your son has a gig in 2 weeks for which he would use this amp? Seems like its late in the 4th quarter, you are 10 points down, looking at a 4th down and 25 after a 15 yard penalty for endangering the relationship with your son. Time to punt. Or at least have a plan B.
I've rebuilt 2 Filmosound 179s. Different beast but also a small difficult chassis. For the first one I used the original chassis and swore up a storm. But I liked the faceplate and the iron, so for the second amp I bought a larger blank chassis, mated up the faceplate and iron, and was much happier.
But, if you go ahead, I hope you prove me wrong!!

[Jerry garrcia]

I see another Filmosound in the background, so you likely know what a pain in the ass this will be. Its a lot of work to do because you like the faceplate.
Your son has a gig in 2 weeks for which he would use this amp? Seems like its late in the 4th quarter, you are 10 points down, looking at a 4th down and 25 after a 15 yard penalty for endangering the relationship with your son. Time to punt. Or at least have a plan B.
I've rebuilt 2 Filmosound 179s. Different beast but also a small difficult chassis. For the first one I used the original chassis and swore up a storm. But I liked the faceplate and the iron, so for the second amp I bought a larger blank chassis, mated up the faceplate and iron, and was much happier.
But, if you go ahead, I hope you prove me wrong!!

In the background there is a 621. Almost a 179. I’ve rebuilt a few of them and I agree. The first one was a PITA but now I know how to do it so it’s not a major hassle. 2h of gutting/stripping then just to rebuild with upping the NFB resistor, changing jacks, adding switches/pilot lights, Coaxes, new power rail … still a lot of time consuming work.
That’s the reason I want to get ideas for a regular board layout for a known circuit. Just build the circuit on a board, drilling and mounting. One input, gain stage, treble and bass tone stack, recovery/simple reverb/driver, pi and output tubes.
A shortcut but hopefully a true one.

[bmccowan]

Understood. Sluckey is the master of compact boards. Have you looked at his projects?
Sluckeyamps.com

[Jerry garrcia]

Understood. Sluckey is the master of compact boards. Have you looked at his projects?
Sluckeyamps.com

Just out of curiosity how do you build your 179’s? I have two more in the basement. I’ve kept the original amp circuit with the local NFB at the V1 (6J7/ef37a), removed one of the output jacks and added a switch to change the output impedance, upped the filtercaps, changed the 22K NFB to a 56K, improved the grounding scheme and added a cathode bypass switch on V1. Sounds really tweedy but better than an 5E3.
But since I have two more one could always do something different on one of them. Since there are two unused sockets (which I use as “tag strips” I was thinking of a one tube reverb. The major drawback with that is more components in that packed chassis and having to drill another hole in thick steel.

[Jerry garrcia]

Understood. Sluckey is the master of compact boards. Have you looked at his projects?
Sluckeyamps.com

Thanks for the link. I actually think I will make @sluckey AC-15 with reverb. https://sluckeyamps.com/misc/AC-15R_Lite.pdf

The problem will be to find a good place for the two extra potentiometers, the reverb and cut.
I can place the 2x33uF and one 22uF in the extra chassis with the PT on and run an umbilical cord to the amp. Thinking of using the 250V PT without a CT and use a sag resistor alternative an artificial CT with silicone diodes and a ez81 rectifier

[bmccowan]

Just out of curiosity how do you build your 179’s?

They are pretty simple. I replaced the top cap 6J7 with a 6SJ7. Used a typical Gibson circuit for the that tube - for the PI and power tubes I went similar to some Valcos I like. Anything I did not use, I stripped out. I used a very small turret board for the preamp and point-to-point for the rest. I call it a Schoolie because of my grade school memories of Filmosound projectors in the classroom.
They sound good, but I find it a trick to get the one in the tiny original chassis as quiet as I would like. Finding the right 6SJ7 helps and I should try a 5693.

[Jerry garrcia]

Just out of curiosity how do you build your 179’s?

They are pretty simple. I replaced the top cap 6J7 with a 6SJ7. Used a typical Gibson circuit for the that tube - for the PI and power tubes I went similar to some Valcos I like. Anything I did not use, I stripped out. I used a very small turret board for the preamp and point-to-point for the rest. I call it a Schoolie because of my grad school memories of Filmosound projectors in the classroom.
They sound good, but I find it a trick to get the one in the tiny original chassis as quiet as I would like. Finding the right 6SJ7 helps and I should try a 5693.

Thanks for the schematic. I have tons of 6SJ7’s. One of my favorite tube. But in the EF37A is so sweet looking and I really like the top cap as a visual thing.
That’s a PI i haven’t seen before. Did you do the math yourself or took it from another circuit? Have you scoped it to see if it delivers an equal Vpp to the 6V6’s?

[Jerry garrcia]

I’ve as usual when something is bugging me been a bit cognitive distracted from the rest of the family. Been contemplating different setups and this AC-15R really appeal to me but the lack of treble and base doesn’t. That’s something that I need in my chassis. So I’d probably go with this modded AA1164 circuit to get a one knob reverb and a LPT PI. Will see how it will behave with el84’s.

[bmccowan]

Thanks for the schematic. I have tons of 6SJ7’s. One of my favorite tube. But in the EF37A is so sweet looking and I really like the top cap as a visual thing. That’s a PI i haven’t seen before. Did you do the math yourself or took it from another circuit? Have you scoped it to see if it delivers an equal Vpp to the 6V6’s?

I agree on the looks of the EF37A - I should locate a couple of them for other projects that use the 6J7s. I'm done with Filmosounds as my arthritis just cannot deal with that tiny chassis. And math? - No I just borrowed from an early 50s Valco circuit. I think it was used in a National branded amp, but likely used in others too. It's been a while - fuzzy memory. I also have not scoped it and Valco PIs are known for being imbalanced (like my mental stability)
Your revised project looks interesting - and ambitious (I mean that in a positive way)

[Jerry garrcia]

So here are the three different circuits that I can’t decide on which to build. Oh the pressure of options. Unfortunately the Vox15R doesn’t have a TMB.

[tubeswell]

Steve’s AC15R will have better reverb. But you might prefer a standard BF input channel (with a TB tonestack sandwiched between two 12AX7 triodes) instead of the EF86

[Jerry garrcia]

Steve’s AC15R will have better reverb. But you might prefer a standard BF input channel (with a TB tonestack sandwiched between two 12AX7 triodes) instead of the EF86

Yep. That’s the problem. It seems like I can’t have them both.
So you think a BF reverb, as the original circuit will work with EL84’s if I change the voltages and Rg and Rg2’s?
And what’s with that NFB loop with the 3m3 resistor instead of the original 3m3 and 10pF cap?

[Willabe]

EF86's often have problems, especially as the input tube. Vox got rid of them and latter added the top boost circuit to make up the gain loss from the EF86 and gave them TB tone stack, which you could add a mid control.

I'd go with what tubeswell said.

And what’s with that NFB loop with the 3m3 resistor instead of the original 3m3 and 10pF cap?

It's -  M for meg, not m for milli.

I've not seen a schematic with a 3M3 R with a 10pF cap across it. Is that in a Matchless amps NFB loop?

If so, the 10pF cap just bypasses the very high end around that 3M3 R. So the very highs get effected way more than the other frequencies that go through the 3M3 R.

 

 

[Jerry garrcia]

EF86's often have problems, especially as the input tube. Vox got rid of them and latter added the top boost circuit to make up the gain loss from the EF86 and gave them TB tone stack, which you could add a mid control.

I'd go with what tubeswell said.

And what’s with that NFB loop with the 3m3 resistor instead of the original 3m3 and 10pF cap?

It's -  M for meg, not m for milli.

I've not seen a schematic with a 3M3 R with a 10pF cap across it. Is that in a Matchless amps NFB loop?

If so, the 10pF cap just bypasses the very high end around that 3M3 R. So the very highs get effected way more than the other frequencies that go through the 3M3 R.

Sorry. Misspelled. Of course meg.
The circuit I referring to is the BF Princeton reverb. Cathodyne PI. There is a builder who made it with a LTP PI and then added the NFB loop to the PI tube with a 3M3 and it’s coming from the wrong phase of the OT secondary.
I just wanted to build an amp with a single input, TB tone stack and a pair of el84’s and got deep in to the rabbit hole. Purpose was to fit in a special small cab with a face plate that I like.
Some says the Princeton reverb doesn’t sound good with el84’s. That’s why I started to look at the Vox-15R and modified PR with LTP. Was hoping for a fast build but it seems to be a larger project.

[Willabe]

The circuit I referring to is the BF Princeton reverb. Cathodyne PI. There is a builder who made it with a LTP PI and then added the NFB loop to the PI tube with a 3M3 and it’s coming from the wrong phase of the OT secondary.

That LTPI it says is from a Matchless Chieftain. He reversed the OT secondaries because he injected the NFB into the input side of the LTPI. He did that because he injected the reverb into the other side of the LTPI where the NFB normally gets injected on a LTPI.

The 3M3/10pF in the Princeton Reverb has nothing to do with the NFB loop. That 3M3 R knocks down the preamp dry signal so it doesn't swamp out the verb's output. The 10pF cap is there to restore a little of the very high end that a very large R will knock out. The larger the value of a series R the more it will kill the very high end.   

I just wanted to build an amp with a single input, TB tone stack and a pair of el84’s and got deep in to the rabbit hole. Purpose was to fit in a special small cab with a face plate that I like.
Some says the Princeton reverb doesn’t sound good with el84’s. That’s why I started to look at the Vox-15R and modified PR with LTP. Was hoping for a fast build but it seems to be a larger project.

So build a single channel Vox AC30 with just 2 x EL84's and the top boost circuit. And add reverb if you want. Leave out that cross line tone and cross line volume just before the EL34's. They don't work very well. And use the BF Fender TS, that Vox top boost ST is a little messed up. (Vox stole it from Gibson and the circuit Vox copied the schematic was draw wrong.)
   

[Jerry garrcia]

The circuit I referring to is the BF Princeton reverb. Cathodyne PI. There is a builder who made it with a LTP PI and then added the NFB loop to the PI tube with a 3M3 and it’s coming from the wrong phase of the OT secondary.

That LTPI it says is from a Matchless Chieftain. He reversed the OT secondaries because he injected the NFB into the input side of the LTPI. He did that because he injected the reverb into the other side of the LTPI where the NFB normally gets injected on a LTPI.

The 3M3/10pF in the Princeton Reverb has nothing to do with the NFB loop. That 3M3 R knocks down the preamp dry signal so it doesn't swamp out the verb's output. The 10pF cap is there to restore a little of the very high end that a very large R will knock out. The larger the value of a series R the more it will kill the very high end.   

I just wanted to build an amp with a single input, TB tone stack and a pair of el84’s and got deep in to the rabbit hole. Purpose was to fit in a special small cab with a face plate that I like.
Some says the Princeton reverb doesn’t sound good with el84’s. That’s why I started to look at the Vox-15R and modified PR with LTP. Was hoping for a fast build but it seems to be a larger project.

So build a single channel Vox AC30 with just 2 x EL84's and the top boost circuit. And add reverb if you want. Leave out that cross line tone and cross line volume just before the EL34's. They don't work very well. And use the BF Fender TS, that Vox top boost ST is a little messed up. (Vox stole it from Gibson and the circuit Vox copied the schematic was draw wrong.)
 

I did actually know that the 3M3+10pf in the original circuit was part of the NFB. Language barrier. Thanks for explaining the rest.

So this is what you suppose? A BF PR reverb and TB tone stack (instead of the Vox one) and with voltages for EL84’s?

[Willabe]

I did actually know that the 3M3+10pf in the original circuit was part of the NFB. Language barrier. Thanks for explaining the rest.

No.

The 3M3/10pF is NOT part of the NFB loop.

It's to balance the dry/wet reverb signal.

[Jerry garrcia]

I did actually know that the 3M3+10pf in the original circuit was part of the NFB. Language barrier. Thanks for explaining the rest.

No.

The 3M3/10pF is NOT part of the NFB loop.

It's to balance the dry/wet reverb signal.

sorry. The “not” fell away when writing. My apologies. In a BF PR I do know the function of the 3M3 +10pF. And it’s not a part of the NFB. My wife got angry when writing on the cellphone instead of reading a book so didn’t have time to check my writing and spelling before posting.

What about the AC30 thing I posted? With a BF PR reverb circuit I just have to add one 12at7.
Or I just go with the original PR w/o tremolo and adopt the voltages and Rp, Rg2 and Rk for el84’s. The easy path

[Willabe]

What about the AC30 thing I posted? With a BF PR reverb circuit I just have to add one 12at7.
Or I just go with the original PR w/o tremolo and adopt the voltages and Rp, Rg2 and Rk for el84’s. The easy path.

Because you wrote this;

Some says the Princeton reverb doesn’t sound good with el84’s. That’s why I started to look at the Vox-15R and modified PR with LTP. Was hoping for a fast build but it seems to be a larger project.

I don't know for sure if a Princeton with EL84's will sound great or not.     It very well could be some guys would love it, other wouldn't, personal taste.

Or, it may be that the guys that like EL84's like the Vox AC30 top boost preamps sound better than the Princeton's preamp?

Or, they want the EF86 sound, many love the sound of an EF86, I don't like it. My friend bought an old AC15 back in the 80's, we plugged into the EF86 channel and we thought it sounded bad. But we were used to Fenders.
 
The top boost circuit does drive the TS with a cathode follower (CF) that will make it sound different than a Princeton preamp that's TS is plate driven.

And Vox AC15/AC30's have no NFB loops. That's a big difference in sound from any amp with a NFB loop.

I'm really the wrong guy to ask about this, I don't like the sound of EL84 amps and I don't like heavy distortion. I listen to some bands/players with it but I draw the line before a lot of guys on how much.

The only guitar player I like who used an AC30 was Rory Gallagher.  And Tommy Malone from the Subdudes used an AC30 for a while, and I loved his sound with it! 

[bmccowan]

And Tommy Malone from the Subdudes used an AC30 for a while, and I loved his sound with it!

Oh yeah! I'm with you on Tommy.
I also am not a fan of the EL84 in guitar amps - love them in stereo amps.
I am fond of 6973/6CZ5 tubes. RCA 6CZ5s are the best to my ears and cost only an arm - no leg needed.
Some assume they sound like EL84s because of the size/shape, but they don't, they are closer to 6V6s.
I've had good luck with Valco circuits but also converting Marshall 18 and Voxy circuits.
Sorry - Willabe's Subdudes note got me going!

[ok_state_blues]

Just out of curiosity how do you build your 179’s?

They are pretty simple. I replaced the top cap 6J7 with a 6SJ7. Used a typical Gibson circuit for the that tube - for the PI and power tubes I went similar to some Valcos I like. Anything I did not use, I stripped out. I used a very small turret board for the preamp and point-to-point for the rest. I call it a Schoolie because of my grade school memories of Filmosound projectors in the classroom.
They sound good, but I find it a trick to get the one in the tiny original chassis as quiet as I would like. Finding the right 6SJ7 helps and I should try a 5693.

@bmccowan PM sent

[Jerry garrcia]

So after a lot of thinking I have decided for the main circuit.
BF PR pre. Insertion of included on tube reverb with a fixed dwell by a resistor and a 18W lite IIB PI and output section. Will probably go cathode bias but will try to have room for a fixed one if needed.
Since the OT I’m planning to use is from an old reel to reel and is w/o CT, has 250V secondaries it will be SS rectification with a 150R, 10W sag resistor.

As previous poster has said I’m not that certain of the el84’s as well. Using them since I have quite a few ones and that it would be fun to try something else than octals. My first amp was a Peavey Classic 30 and I never got to love it. I actually still got it. Brought it up from the cellar yesterday to give it a look through before I was going to sell it. It was actually the first amp that I used a soldering iron on. Needed to put in a power soaker for my son. Didn’t like the sound of it and he was into bebop jazz. Wanted a Gibson GA-20. Since i wasn’t going to spend that amount of money on the spoiled brat i decided to build one. So here I am 5 years later with our rosewood sideboard filled with all kinds of octal preamp tubes and half build amps and the basement storage filled with old projector speaker cabinets and Filmosound amps, tweaked early Gibson circuits (that’s why I never used the LTP before, mostly using the paraphase (and cathodyne in Filmosound conversions)). Probably have 4-5 different Filmosound 621/179’s and as many variants of the GA-5 Les Paul jr and othe two channel designs in a 5f2A chassis.

Need to sell a few I guess but really don’t know how. eBay, reverb?

Anyway thanks for the help and encouragement. I’ll update when done with some gut shots and sound clips.

[ok_state_blues]

@Jerry garrcia pm sent

[Jerry garrcia]

I think I go with this one. Any inputs is greatly appreciated!