Throwing metal film resistors in Fender amps

[soundmasterg]

Hello Greg !
Thanks for the answer. What do you recommand for the vibrato channel tone stack caps, then ? The blue molded Sozo are out of my budget and out of my range.
What would you choose between : Jupiter, Mallory 150s, OD 225P, 715 or 716, Sozo Mustard, Cornell Dubilier, Roederstein MKT1813, ... (see all caps at https://www.tube-town.net/ttstore/in...apacitors.html or Capacitors :: Passive Components :: Electronic Parts :: Banzai Music GmbH)
And do you think my small modification for a stereo jack footswitch might work ?

Well the Blue Sozos would be my choice for a modern cap replacement in a blackface Fender type build since they are made to emulate the old blue molded Mallorys.....they are cheaper than the Jupiters....I've used them in a few rebuilds of vintage Fenders and they sound very much like the original caps.

Mallory 150's are good caps and would sound fine....likewise the Sozo Mustards....and a lot of others. I would stay away from 715 or 716P as they are polypropylene caps. The originals were polyester, and any polyester cap will get you closer to that vintage sound than polypropylene. The 225P are film and foil polyester. The Sozo Mustard are also film and foil polyester. The M150's are metallized polyester.

A good thing to do is to mix and match....so say Sozo blues for most of the vibrato channel but use OD 225P's in the phase inverter or something like that. There is a difference in sound between various caps, but it is more the difference between the dialectric type and the way it is made rather than the brand per se. So for instance a film and foil polyester will sound a bit different than a metallized polyester, and they will both sound different that polypropylene. Make a decision and pick something and you can always change it out later...caps are cheap relatively speaking. You will notice more difference in sound by changing speakers or tubes than you will be changing caps. The main thing is to get something in place that is good quality and all of the brands you listed above are that.

Greg

[Wombaticus]

Hello Greg !
Thanks for the answer. What do you recommand for the vibrato channel tone stack caps, then ? The blue molded Sozo are out of my budget and out of my range.
What would you choose between : Jupiter, Mallory 150s, OD 225P, 715 or 716, Sozo Mustard, Cornell Dubilier, Roederstein MKT1813, ...

It doesn't make a damned bit of difference which of these caps you put in, so long as they have the right value and voltage rating. The tonal variation will be non-existent or so tiny as to be inconsequential. Mallory's are compact and fairly inexpensive, so I end up using them a lot.

[Wil]

Hey everyone,

I ordered all the parts to create my own AB763 hoffman board but I now have some question regarding the filter cap wiring design.

On the regular deluxe ab763 schematic I see 2 resistors between, respectively, BC and CD. They both are 10k (high wattage).
But on the hoffman deluxe ab763 schematic they are respectively 1k and 4.7k. Why ? What would be best for a deluxe reverb ?

I made a mistake while ordering. I got 2x16uf 475V instead of 5.
Since I have 3 22uf F&T, I'll make a mix of those.
The original deluxes used 16uf and I want to be as vintage correct in terms of component values as I can.
Where do you think I should put the 2 16uf ?

Last question (and I rather feel stupid 5 min than really be if I fry my amp by not asking), negative sides of all filter caps go to ground, right ?

Thank you in advance for your answers.

[g1]

Bias caps should be positive end to ground.

[Wombaticus]

Hey everyone,

I ordered all the parts to create my own AB763 hoffman board but I now have some question regarding the filter cap wiring design.

On the regular deluxe ab763 schematic I see 2 resistors between, respectively, BC and CD. They both are 10k (high wattage).
But on the hoffman deluxe ab763 schematic they are respectively 1k and 4.7k. Why ? What would be best for a deluxe reverb ?

I made a mistake while ordering. I got 2x16uf 475V instead of 5.
Since I have 3 22uf F&T, I'll make a mix of those.
The original deluxes used 16uf and I want to be as vintage correct in terms of component values as I can.
Where do you think I should put the 2 16uf ?


Thank you in advance for your answers.

Stick with the 10K, 10K. With those 16uF caps, you'll get a respectable 1Hz corner frequency on the filter with a 10K resistance in front of it, but a downright regrettable 10Hz with only 1K.

Use the 22uF caps in the reservoir and screen grid nodes.

[Wil]

Bias caps should be positive end to ground.

Are you sure ? None of the schematics I saw got it that way.

Stick with the 10K, 10K. With those 16uF caps, you'll get a respectable 1Hz corner frequency on the filter with a 10K resistance in front of it, but a downright regrettable 10Hz with only 1K.

Use the 22uF caps in the reservoir and screen grid nodes.

Do you confirm the positive side toward ground filter caps design ?

According to this :
http://www.el34world.com/Hoffman/ima...TwoChannel.gif
and this :
http://www.thevintagesound.com/ffg/s...b763_schem.gif
It is unlikely.

(and can you tell me which, on the layout, are the "reservoir" and "screen grid node", these are terms I have difficulty to translate)

[Enzo]

Look at the schematics you just linked. The Deluxe reverb AB763 for example. The bias suspply is just above the GZ34, note the 25uf 50v filter cap with the + end to ground.

Now look at the wiring layout you posted from Hoffman. See the bias supply, upper right, where it says bias range resistor. The bias control and hte little pink 12 in a box, there is the bias supply, and once again, note the 47uf cap has the + end to ground.

The only schematics that show the BIAS filter cap with the negative end grounded are drawings with mistakes.

[g1]

I said bias cap was positive to ground. It is the only one. On your layout it is shown as a 47uF at the bias pot. + end is grounded.
On same layout drawing, the 2 caps on the right of the choke are reservoir, the one to the left of the choke is the screen grid node.

[soundguruman]

Hey everyone,

I ordered all the parts to create my own AB763 hoffman board but I now have some question regarding the filter cap wiring design.

On the regular deluxe ab763 schematic I see 2 resistors between, respectively, BC and CD. They both are 10k (high wattage).
But on the hoffman deluxe ab763 schematic they are respectively 1k and 4.7k. Why ? What would be best for a deluxe reverb ?

I made a mistake while ordering. I got 2x16uf 475V instead of 5.
Since I have 3 22uf F&T, I'll make a mix of those.
The original deluxes used 16uf and I want to be as vintage correct in terms of component values as I can.
Where do you think I should put the 2 16uf ?

Last question (and I rather feel stupid 5 min than really be if I fry my amp by not asking), negative sides of all filter caps go to ground, right ?

Thank you in advance for your answers.

F&T sound better, FYI.
Original was 25uF for bias filter cap.
Increase bias filter to 47uF "can" cause (may cause) low frequency distortion, but if that happens you will probably notice low frequencies sound muddy.

Tried this in 67 Princeton, the other day...
used 100uF for bias filter cap....Lows sounded like pure MUD.
Changed back to 33 uF and it was CLEAN.
Original was 25uF...

Moral of story: Over-sized Bias filter cap can cause low frequency distortion.
The factory selected that value bias filter cap for a REASON.
While there are many who don't agree, my ears DO NOT lie. I CAN hear the distortion.

Marshall super lead has 8 uF bias filter caps.
Why not 100? You tell me.

I am thinking the bias filter was selected for the same reasons as I have given...
but I will never know for sure.

[tedmich]

I wouldn't say the 225P's are that close to the old blue molded mallory caps that Fender used in their blackface stuff. The handmade Sozo blues are probably closer...at least to my ears, and they are marketed that way too. I've used them in a couple amps for people and they sound spot on, but sound is subjective as everyone knows so YMMV. Fender used some blue caps in the early to mid silverface stuff also so you have to specify which old blue fender caps you are talking about. These were excellent caps too btw....the bad ones were the brown terds that were used in some late blackface/early silverface stuff. They were lousy caps from the beginning.

Mojo and hype are fine, but its best to try before you form an opinion.

Sozo? I cant resist...

[soundmasterg]

I have only used the old Sozo mustards and the Sozo blue caps myself and have got good results from them. They sounded slightly different than an M150 for example, but as with all coupling cap changes within a given type (polyester to polyester) the changes were very slight between the Sozos and M150's. I never tried their electrolytic caps that they sold (apparently no longer sell) or the handmade mustards and I never bothered with the hype. I tried them and they worked and sounded fine...I'm sure many others would also work well too.

Funny video tedmich. I'm not sure where you got all the litigation stuff you mentioned in the video...maybe I missed some of it on the web or something....

Greg

[soundmasterg]

I have only used the old Sozo mustards and the Sozo blue caps myself and have got good results from them. They sounded slightly different than an M150 for example, but as with all coupling cap changes within a given type (polyester to polyester) the changes were very slight between the Sozos and M150's. I never tried their electrolytic caps that they sold (apparently no longer sell) or the handmade mustards and I never bothered with the hype. I tried them and they worked and sounded fine...I'm sure many others would also work well too.

Funny video tedmich. I'm not sure where you got all the litigation stuff you mentioned in the video...maybe I missed some of it on the web or something....

Greg

[Wil]

I said bias cap was positive to ground. It is the only one. On your layout it is shown as a 47uF at the bias pot. + end is grounded.
On same layout drawing, the 2 caps on the right of the choke are reservoir, the one to the left of the choke is the screen grid node.

Oh sorry, I read filter caps. I'm having loooong working days and my mind is flat at the end of the day.
Thank you for your input. I'm amazed by the knowledge that shines out of this forum...

I received the parts I need and am really excited to start the build !
I'll keep you informed of my building process and story. But I doubt you will find something new in this, haha!

Have a nice day everyone,
Romain from Belgium. (Luxembourg for the moment actually, haha!)

Post-Scriptum: Parts are :
Roederstein MKT1813, Jupiter, OD 6PS (vibrato channel) and 716P (normal channel) caps, RN65D and standard 0,6W metal film resistors.

[tedmich]

the video is a verbatim rendering of an interaction with the founder of Sozo and a forumite who called him on his BS. The guy may sell decent caps but he's a bit of a douche.

[soundmasterg]

the video is a verbatim rendering of an interaction with the founder of Sozo and a forumite who called him on his BS. The guy may sell decent caps but he's a bit of a douche.

I've never intereacted with the Sozo guy personally....I've just used some of the caps and I like the caps.

When you're in business sometimes you have to take a stand against stuff to avoid worse stuff that can affect your business, or slander that isn't true. It happened to Ted Weber when he had to go after the 18 watt forum, and then TA got burned with the Scumbag speaker stuff. I think in both cases they handled it well to protect their businesses and cause the least damage otherwise. We don't know the circumstances behind the Sozo thing, so I prefer not to comment on any of it unless I find out more facts.

Greg