Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: valvetones on February 28, 2022, 11:11:38 pm

Title: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:11:38 pm

Pretty Groovy. Need to build the head cabinet and speaker cabinet.
Reforming the caps worked like a charm.
Few pics from the process.
I did change the reverb driver to an old fender one. And the EF86 coupling caps where made larger.
The vibrato channel B+ was coming back to the tone pot, so I added a cap after the tone pot which put the two caps in series which cut the capacitance in half , which made the tone control not roll off much.
So changed the EF86 plate cap and cap after the tone control from .0033 to .068.
Much better.

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:12:39 pm

Reforming the old caps worked like a charm.

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:15:07 pm

Transformers fit like a glove.
Triad output
Stancor power (used a zener to get the B+ perfect)
Triad choke.
Noice!!

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:18:27 pm

One curiously though.
Did the Vibrato on the 6G16 work on the normal channel too on original fenders?
It does on this one, which I thought maybe had to do with the EF86 normal channel, but then checked my other VV build, and it works on that normal channel too.
Pretty sure I got it right.
Just surprised that the vibrato works on the normal channel.

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:22:43 pm

On the original VV it has two 16mfd caps in parallel for the reservoir.
I just used one 30mfd cap.
And didn’t have all the 16mfd caps I needed , so the last node I used two 8mfd in parallel.
So things kinda shifted on the cap board.
Just in case it looks weird to anyone.

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:30:50 pm

The ceramic switch got changed from the Lil one to the big one.
Barely fit. But now I can switch between 4/8/16 if needed.
Good rotary switches are kinda hard to find. I was surprised!

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:38:14 pm

So the triad OT is an SX-201
3300 ohm primary.
So the big head scratcher now is
6L6’s, EL34’s or EL37’s
I’m deliberating
Leaning towards the EL37’s though.

I have a pair of WE350B’s laying around too, but I don’t know if the screens on those would tolerate the voltages, and I don’t wanna find out that they won’t if y’all know what I mean. That would be a somber moment.
I think the EL37s with a mess of telefunkens in the preamp may be the ticket.

Title: Re: EF86 Vibroverb
Post by: valvetones on February 28, 2022, 11:41:32 pm

Oh I almost forgot, because of this 8 ohm decision below, does anyone know if I need to tweak the NFB resistor values since the original 6G16 ran on a 4 ohm setup?

Title: Re: EF86 Vibroverb
Post by: sluckey on March 01, 2022, 06:04:33 am

Quote from: valvetones on February 28, 2022, 11:18:27 pm

Did the Vibrato on the 6G16 work on the normal channel too on original fenders?

yes

Quote

Oh I almost forgot, because of this 8 ohm decision below, does anyone know if I need to tweak the NFB resistor values since the original 6G16 ran on a 4 ohm setup?

Not necessary. Just connect the NFB circuit to the 4Ω tap on your multi-tap OT.

Title: Re: EF86 Vibroverb
Post by: valvetones on March 01, 2022, 01:43:14 pm

Thanks Slucky.
Stay awesome myfriend.