FILMOSOUND REBUILT

[jujudublues]

Hi !

I managed to buy a filmosound pretty cheap and gutted it to rebuild a 5E3 in there.
I already read a lot about how the 5E3 character can't be simplified to a simpler vol / tone circuit because of the interactive channels.
Still i really want stick with the Filmosound layout : 1 input, 1 volume, 1 tone.

I mocked up this scematic :
- single channel 5E3 à la 5E5
- switch to parallel the 12AY7 ( worked well on my PA 26-66 )
- might try a 6SL7 in there as preamp since the chassis already drilled for that.

Let me know of you guys see any mistakes - i amp open to suggestions too.

One last thing i measured the transformers with my limited skills and can share that too.

Cheers and happy new year !

[kagliostro]

I begin to look to the schematic at the input

First thing I noticed, to me the switch to connect the two triodes in parallel must have the center connected to the grid of the second triode, not the first one

Franco

[jujudublues]

Hi Franco

thank you.
My mistake - you are right - here is the updated schematic

Thank you a lot

[bmccowan]

Juju - I assume your amp is a 179 model? If so, all of your tube sockets are octal? If so, I suggest you consider 6SL7s for both V1 and V2. Or V2 can be 6SC7 or 6SN7. The 5b6 Bassman is a good schematic to use for amending for your project as it uses the 1 volume 1 Tone you are seeking. The power amp is pretty much the same as for the 5e3, just 6L6 instead of 6V6.
Paralleling V1 should be no problem. Getting a quiet amp with that tiny chassis can be a challenge. There are some shields in the original chassis, leaving them in place helps I think. There is also an extra octal socket in the 179, makes for convenient connection tags.

[jujudublues]

hey bmccowman -

thanks for the input
it is a 179, all octal and i might try octal preamp option on this build - either PI / preamp or both as you said ...
I've been looking at the 5B6 too ... so much that i felt i would build one as my next project, do you think i can switch to 6V6 - 5Y3 without much modifications to the circuit ? i've heard the 5B6 is sensitive to layouts ...
i kept the shields between power and preamp ...
I plan to draw a clean layout of whats planned ...

Thanks for the inputs !

[bmccowan]

I've been looking at the 5B6 too ... so much that i felt i would build one as my next project, do you think i can switch to 6V6 - 5Y3 without much modifications to the circuit ?

Oh Yeah - easy. You could use the standard filter/power rail and 5Y3 of the 5E3 Just as you have it in your schematic, or you could increase the value of the filter caps to 20uf. You could add the 1.5K grid stoppers on the 6v6s.
For the PI, you could use either the schemes from the 5B6,  5E3, or 5C3. I've used the one from the 5C3 with a 6SL7 or 6SN7 in V2. Works fine.

i've heard the 5B6 is sensitive to layouts

I am kind of surprised at this, but the 5B6 is a split chassis with an umbilical cord - so it just might be separation anxiety. Those tweed circuits are pretty damn simple so I do not think layout will be much of a problem as long as standard practice of routing wires and grounding are followed.
And for the preamp you can use the 6SL7 the same way as the 12AY7. It's a great sounding preamp tube IMO.

[jujudublues]

hey bmccowman,

will follow your advice and keep the filmosound project all octal and 6SL7 !
i updated my schematic with the right pinouts ... let me know if you see any mistakes ...
I will come up with a nice layout !

really feel like building a 5B6 as my next project.
I thought you had to be extra careful with the P2P layout to make it silent - not so noisy ...

thank you again !

JUJUJUJU

[jujudublues]

LAYOUT STARTED ... 

[bmccowan]

I thought you had to be extra careful with the P2P layout to make it silent - not so noisy ..

Yes, but that's not exclusive to the 5b6 or any other particular amp. Although there are other factors, high gain and complicated circuits require more careful layout and shielding. The early tweed circuits are simple and fairly low gain.
But layout principals are still in play. keep high V wires away from low V wires (heaters, inputs, etc.) and when they have to cross, try to do it at 90 degree angles. Use a proven grounding scheme. Its the tight Filmosound chassis that makes this difficult, so its great that you are starting with a layout plan.
BTW - here is a good page on parallel triode inputs. 6SL7 is so close to a 12a_7 that all applies.
https://www.ampbooks.com/mobile/amp-technology/parallel/

[Jerry garrcia]

Or you could go with the original amp inside there which sounds great and really “tweedish”. I built this a couple of times and it’s a great sounding circuit. I would up the NFB resistor to a 56K or put a 10K resistor in series with a 100K pot. The EF37A is a substitute to a 6J7.
There is a good place in the front to add a mini toggle switch for a cathode bypass cap switch.

[jujudublues]

bmcowman,

thanks for the advices - i started drawing the layout and in a way, the point to point typology seems easier to work with in such a small chassis ...
will keep you posted.

[jujudublues]

jerry garcia,

thanks for the schematic.
My first option was to try to keep as much as i could of the original amp ... but my filmo was in such a bad shape when i got it that i decided ti simply gut it, some tubes were litterally broken into sockets, rust everywhere...

Thanks anyhow.

[kagliostro]

I don't know exactly what you mean saying PtP

real PtP is this (VOX AC4 Original Layout)



My council is you use Tag Strips on your build (Rebuilded Pathfinder)



Franco

[jujudublues]

Franco,

i am trying to plan a true point to point layout. ckecking components leads length to do so ...
Might need to drop a few strips in there ... The chassis is so small ...

Thanks

Ju

[bmccowan]

Whether you go true PtP or use some tag strips, you are smart to be laying out in detail the plan and posting it here before moving on. It is crowded in there! That Pathfinder layout is nice, but that's a soccer field compared to the Filmosound's Pickleball court. I added some tag strips and single tag points to mine. Best places for those will become clear as your plan comes together.
And then - build carefully. Double check everything, as getting in there to fix errors is a big PIA.
BTW - the original circuit in both of mine sounded like crap with guitar. Whether it was the nature of the circuit or failed/drifted components, or both, didn't much matter as I would rather have given myself a tattoo with my soldering iron than try to troubleshoot in that crowded mess. I do think the pentode preamp is part of the sound, and I kept that, but many have rebuilt with a dual-triode preamp and been happy with the results.

[Jerry garrcia]

jerry garcia,

thanks for the schematic.
My first option was to try to keep as much as i could of the original amp ... but my filmo was in such a bad shape when i got it that i decided ti simply gut it, some tubes were litterally broken into sockets, rust everywhere...

Thanks anyhow.

I have totally gutted the amps before rebuilding. Used the unused tube sockets as connection points like tag strips. Had to attach a few more and reused the small tag board between the power section and the output tubes/preamp tubes.
The filter caps will fit perfectly by the PT. One problem is if you want to use two 1/4” output jacks. One will be hard to place due to the close proximity of one of the 6V6’s. I used a mini toggle switch to be able to use both 8 & 16 ohm speakers.
This is my first rebuild of the original circuit but added a lot of shielded wires and used large pio tone/coupling caps so really crowded. I might give you an idea on where to place some components if you decide PTP. There is also a three part article about a conversion in one guitar magazine available online.

[kagliostro]

One big problem with PtP is where you connect to ground the components that require, multiple ground connections to the chassis is really an easy way to have problems

Better to use a Tag Strip layout or a mix of Tag Strip & PtP to avoid multiple ground connections

An alternative is a Bus Bar ground

Franco

[Jerry garrcia]

One big problem with PtP is where you connect to ground the components that require, multiple ground connections to the chassis is really an easy way to have problems

Better to use a Tag Strip layout or a mix of Tag Strip & PtP to avoid multiple ground connections

An alternative is a Bus Bar ground

Franco

In my spaghetti 621 build I actually  ended up with three grounds but it ended up with to many wires. One MSE, one HV 0V DC (power ground) and one signal ground on a bus (as in the original amp). In the original “layout” the signal ground had a dedicated bus but the HV0DV ground was in multiple places.
In my build after the first I added an isolated node to collect all grounds for the HV0DC, routed it and used a dedicated ground at the negative side of the tag strips for the power section. The preamp filtercaps were grounded at the signal bus. Isolated output jack that was grounded at hv0DC ground and elevated heaters to the cathode of an output tube.
In my experience the most important is to ground the output jacks to the HV0DC ground and elevated heaters, either on the cathode in a cathode biased amp or a dedicated circuit for elevated heater ground up to 40-60V.
Or use a star ground with a bus bar.
But sometimes when duplicating an old PTP circuit I’ve hit a total hum free amp although I’ve used 5-8 ground points

To the OP. You could always add a tremolo or a reverb circuit if you want to use the unused 6V6 socket.
I totally agree with what bmccowan wrote. The pentode up front is a good idea since it sounds glorious. Either with the stock 6J7/EF37A or with a 6SJ7

[bmccowan]

I used 2 ground points in my Filmos a bus grounded near the input for the preamp and a star near the PT for the power amp.
But:

But sometimes when duplicating an old PTP circuit I’ve hit a total hum free amp although I’ve used 5-8 ground points

I have encountered the same many times. Some old amps have grounds anywhere/everywhere - inappropriate I know but I call those slut ground circuits. If the amps are quiet I have learned to leave the grounds as is.

[kagliostro]

Yes, of course, there are multi ground connected amps that are silent but if possible building from scratch it will be better to prevend critical situations

Who knows if those old amp layout were the result of many try and error ?

Elvira Coot (Grandma Duck) said: Better one hectogram of prevention than one kilogram of remedy 

Franco

[jujudublues]

hey -

thanks a lot for all the inputs ...
here is what i'm coming up with so far ...

i think i need to move the 3 large filter caps next to the PT ...
It might be easier too, to move the 2 6v6
Thinking about grouping the 2 6v6 and the PI ...

thanks again .

Ju

[Lectroid]

I rebuilt a 179 as my first amp.  I did not make it a 5E3 clone, (despite the name of my schematic), just cleaned out the hideous tone circuit and rebuilt it to factory spec with the addition of a 5E3 tone stack.  Otherwise I left the tube lineup and passive component values exactly the same.  Having played the result, I wouldn't dream of gutting another one, just to shoehorn in a 5E3.  Your choice, but the 179 is just a different topology with its own distinct charms.  I like the amp's clean sound a lot, and there is a nice Deluxe-like  OD starting around 5 on the volume.  Why do all that work just to build another 5E3? 

So I say: keep that pentode preamp; it's a big part of the amp's sound imo.  I swapped the 6J7 for a 6SL7 which is identical but less microphonic.  I found that putting a couple of O-rings around the 6SL7 dampened any microphonics to nothing. 

My 179 came with a 5Y3 rectifier.  I did use a 22uf-22uf can cap for the reservoir and first filter caps.  Put it above the chassis with the tubes and get that much more space where you need it. The bigger caps values  also stiffen the sound nicely to my ear.  I'm not a fan of heavy sag.   Also: consider removing those metal shield pieces.  I took mine out right away and don't regret it.  More room to work.

[bmccowan]

Lectoid, I think you have a typo. The 6SL7 is not the same as the 6J7. Its the 6SJ7 that is the same - but without the top cap. Your schematic is correct I believe.
That's pretty close to what I built and I agree the pentode preamp gives the amp a different character, similar to some of the early tweed era amps.

[Lectroid]

Bmc:  you are correct. The tube I meant was the 6SJ7. Thanks for the catch.

[jujudublues]

You guys rock !
I will check the schematic and try to work around the 6J7.

Thank you -

[Lectroid]

Remember my mistake:  the tube you want in that slot is the 6SJ7. Less microphonic. Get some heat-resistant O-rings. I bet you’ll like the pentode preamp once you hear it.

[bmccowan]

There is also a premium version of the 6SJ7 - the 5693. They were produced for critical and abusive service. They tend to be less microphonic than the standard 6SJ7. They are more expensive, but still easy to find on eBay. The RCAs are red and look cool - which is really the whole point, eh?

[Lectroid]

The RCAs are red and look cool - which is really the whole point, eh?