NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

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JSett
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Thu Jan 13, 2022 1:48 pm

Argh, my joy was short lived on this. Took it to its first band practice... Fired it up and immediately got a horrible noise. Looked around the back - tubes blue as hell and redplating badly :fp: worked fine before I left the house. 5 mile trip and it's borked.

Typically, no spare 6L6 to hand to see if it's something simple.

I did quickly check them with my Bias Rite when I got home and they're drawing 60mA-ish on standby and when you flick the switch it skyrockets into numbers the Bias Rite can't display. Something's not right. Both of them are equally blue and red and acting as bad so my guess is something inside has gone awry.

*EDIT: it just occurred to me my HRD has 6L6s, so I'll swap those in tonight and see if the problem persists
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by Sauerkraut » Fri Jan 14, 2022 2:17 am

From your description, I think there's a pretty high chance you're about to ruin another pair of 6L6s.

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JSett
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Fri Jan 14, 2022 3:26 am

Sauerkraut wrote:
Fri Jan 14, 2022 2:17 am
From your description, I think there's a pretty high chance you're about to ruin another pair of 6L6s.
Possibly, yeah. I'm going to check the voltages on the pins before I put them in, just to be sure it's nothing really crazy.

I've had a poke around with a chopstick and nothing seems to have come loose on initial inspection. I'll check the resistors etc while I'm there too.
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by Sauerkraut » Fri Jan 14, 2022 6:37 am

johnnysomersett wrote:
Fri Jan 14, 2022 3:26 am
Sauerkraut wrote:
Fri Jan 14, 2022 2:17 am
From your description, I think there's a pretty high chance you're about to ruin another pair of 6L6s.
Possibly, yeah. I'm going to check the voltages on the pins before I put them in, just to be sure it's nothing really crazy.

I've had a poke around with a chopstick and nothing seems to have come loose on initial inspection. I'll check the resistors etc while I'm there too.
Not that I know enough to be advising anyone, and you probably know more than I do, but... does it have adjustable bias? If yes, I'd set the bias pot as cool as possible, then turn to Rob Robinette's website for instructions on red plating.

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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Fri Jan 14, 2022 6:54 am

Sauerkraut wrote:
Fri Jan 14, 2022 6:37 am
johnnysomersett wrote:
Fri Jan 14, 2022 3:26 am
Sauerkraut wrote:
Fri Jan 14, 2022 2:17 am
From your description, I think there's a pretty high chance you're about to ruin another pair of 6L6s.
Possibly, yeah. I'm going to check the voltages on the pins before I put them in, just to be sure it's nothing really crazy.

I've had a poke around with a chopstick and nothing seems to have come loose on initial inspection. I'll check the resistors etc while I'm there too.
Not that I know enough to be advising anyone, and you probably know more than I do, but... does it have adjustable bias? If yes, I'd set the bias pot as cool as possible, then turn to Rob Robinette's website for instructions on red plating.
Yeah, it has a bias pot. I'll go through all my usual procedures to minimise potential for something exploding. Fortunately the supply and bias circuit for these is relatively straightforward
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JSett
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Fri Jan 14, 2022 1:27 pm

Only had a short time tonight to look. The plate and screen read the right numbers, cathodes all good, control grid/bias voltages are wild - but I have been testing with the tubes out as the ones I have are cooked. Checked through most of the components in the power supply section and continuity on ground points. No obvious issues.

I think I'll have to sacrifice some old, but known good, tubes in order to test properly
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by Larsongs » Sat Jan 15, 2022 7:40 am

If you have old vintage Tubes you should save them… You might be better off buying a cheap Set & blow them up!

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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Sat Jan 15, 2022 7:42 am

Larsongs wrote:
Sat Jan 15, 2022 7:40 am
If you have old vintage Tubes you should save them… You might be better off buying a cheap Set & blow them up!
Nah, they're only modern ones, nothing fancy
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by Larsongs » Sat Jan 15, 2022 10:52 am

johnnysomersett wrote:
Sat Jan 15, 2022 7:42 am
Larsongs wrote:
Sat Jan 15, 2022 7:40 am
If you have old vintage Tubes you should save them… You might be better off buying a cheap Set & blow them up!
Nah, they're only modern ones, nothing fancy
In that case go for it… I’m curious to know what the problem is…

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JSett
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Sun Jan 16, 2022 2:36 am

Larsongs wrote:
Sat Jan 15, 2022 10:52 am
johnnysomersett wrote:
Sat Jan 15, 2022 7:42 am
Larsongs wrote:
Sat Jan 15, 2022 7:40 am
If you have old vintage Tubes you should save them… You might be better off buying a cheap Set & blow them up!
Nah, they're only modern ones, nothing fancy
In that case go for it… I’m curious to know what the problem is…
viewtopic.php?f=10&t=121401&p=1705371#p1705371
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by JSett » Mon Jan 17, 2022 11:01 pm

Now I've managed to repair this I've spent more time playing through it. Man, I forgot how good an old twin Fender can sound....big, round and drippy. Absolutely lovely. Just a shame they're so damn heavy!

I think I'll keep this until an appropriate Vibrolux pops up. I know I'll prefer the smaller one but this will happily occupy the spot for now, and it doesn't owe me much money either.
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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by Sauerkraut » Tue Jan 18, 2022 6:04 am

At the risk of veering off-topic... Wouldn't it make a whole lot of sense for Fender to (finally) introduce a Vibroverb head? Perhaps with a vintage-voiced, blackface channel and a less mid-scooped, earlier break-up "lead" channel, plus a built-in attenuator like on the Tone Masters. Or just one channel, but with mid control and master volume. AB763 circuit, 40 watts, with tube-driven reverb and tremolo, all in a head that you then get to pick your favourite speaker cab for... what more could anyone want? As far as I'm aware, Fender offer 0 amp heads at the moment. I don't think I'll ever understand why head + cabs aren't way more popular than combos.

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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by Sauerkraut » Wed Jan 19, 2022 3:34 am


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Re: NAD: What do you reckon it is?...SOLVED: SF Pro Reverb

Post by hexes » Mon Jan 24, 2022 1:17 pm

Sauerkraut wrote:
Wed Jan 19, 2022 3:34 am
Oh shit... This actually exists!
I have a fresh repro brown vibroverb chassis i’ve been wondering what to do with. some good ideas in your previous post.

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