Deluxe Reverb Reissue - Hiss

[earache]

Hello and Happy New Year all!

I’m looking at a Deluxe Reverb Reissue that has a noticeable hiss. I’ve replaced all of the tubes individually with known-good ones and this has made no difference.

Is this a common problem with this reissue? Anybody had this problem before?

I should mention that it is a relatively new (less than two years) Silverface Reissue.

Thanks in advance

[nosaj]

Hello and Happy New Year all!

I’m looking at a Deluxe Reverb Reissue that has a noticeable hiss. I’ve replaced all of the tubes individually with known-good ones and this has made no difference.

Is this a common problem with this reissue? Anybody had this problem before?

I should mention that it is a relatively new (less than two years) Silverface Reissue.

Thanks in advance

Try this now to isolate. Remove the first tube(12ax7) is hiss still there? yes remove 2nd tube is hiss still there? yes go to tube 3 and so forth.

Whereever the hiss stops when a tube is removed the problem will be in the part of the circuit from that tube going back to input.

nosaj

[Jazz P Bass]

Or, turn the controls.

Do any of them affect the 'hiss'?

[Tone Meister]

Please post a schematic.

If you have the expertise, check to see if the negative feedback resistor is 820R. If it isn't, install an 820 ohm resistor in place of the existing NFR.

Does it hiss worse when the reverb is turned up? If so, try flipping the reverb tank horizontally 180 degrees in the cabinet and see if that helps.

[earache]

The hiss increases when turning either volume knob up, no other knob affects the hiss, although thereÂ’s increased hum when the reverb control is maxed.

IÂ’m looking for a schematic. Turning the reverb tank 180 degrees does nothing to affect the hum.

Nosaj - in reply to your post as to removing tubes 1 at a time:
Removing V1 = no hiss at channel 1
V2 = no hiss at channel 2
V3 = maybe less hiss channel 1?
V4 = no hiss, no sound, no nada
V5 = no change at all
V6 = same as V4

[nosaj]

The hiss increases when turning either volume knob up, no other knob affects the hiss, although thereÂ’s increased hum when the reverb control is maxed.

IÂ’m looking for a schematic. Turning the reverb tank 180 degrees does nothing to affect the hum.

Nosaj - in reply to your post as to removing tubes 1 at a time:
Removing V1 = no hiss at channel 1
V2 = no hiss at channel 2
V3 = maybe less hiss channel 1?
V4 = no hiss, no sound, no nada
V5 = no change at all
V6 = same as V4

What are the controls set at and is there an instrument plugged in?
https://www.thetubestore.com/lib/the...-Schematic.pdf
nosaj

[Tone Meister]

If you have the expertise, check to see if the negative feedback resistor is 820R. If it isn't, install an 820 ohm resistor in place of the existing NFR.

Please check the value of the negative feedback resistor

[Justin Thomas]

Please note, these "68 Custom" series are not reissues. They are not faithful recreations of a 1968 Fender circuit (which would be hilarious, since it was supposedly the ---68 series which gave the SF amps their bad reputation). They are "vintage modified," having several gain-boosting features that techs have been adding for decades, along with reverb on both channels, etc. And gain => hiss. These are known for being hissier than their vintage or reissue counterparts.

Service manual here:
https://www.manualslib.com/manual/10...xe-Reverb.html

'm not saying the amp is not broken, but I am saying that it has several "hiss-boosters" built in.

Justin

[pdf64]

It’s been reported here that the additional grid stoppers fitted to these models are a significant source of hiss. Maybe try tack soldering links across them to check that on yours. I can’t make out their details on the linked schematic but seem to remember they’re 10k.

[g1]

Yes they are 10K grid stoppers on the preamp tubes.
Maybe this schematic is easier to read (pg.12 of pdf)

[pdf64]

Hmm, note 14 seems to say they're (R117,118,119,120,121,122) fitted to export models only?
Doh, I was using my iphone to try and read the schematic Justin linked to, and didn't notice the magnifier or download options.

[g1]

Hmm, note 14 seems to say they're (R117,118,119,120,121,122) fitted to export models only?

Or maybe fitted at the tube sockets rather than the board?
The wording is a little awkward:
"components installed at chassis assembly for non-domestic models only"

[Tone Meister]

The NFR on some of these new Fenders is a non-traditional value and can be the source of considerable idle hiss.

[earache]

Tone Meister

Finally got back to this, and installed an 820 ohm negative feedback resistor in place of the factory 15K. This change really did improve the noise floor of the amp.

I elected to not change the grid stoppers.

i can see what you folks meant when you said it has some mods for gain. It even has added shielding over the power tubes, in the form of a cage attached to the back panel.

Thanks again for your help everybody, you guys are the best!

[Helmholtz]

If the hiss stops when you short the hot side of the intensity pot or the lower end of R35 to ground (using a short lead), the source of the hiss is not in the power amp.

Replacing the 1.5k NFB resistor with 820 Ohm reduces power amp gain by a factor of around 2. As a result also the hiss will be somewhat less. But the 820 Ohm resistor also increases the feedback ratio and thus the risk of instabilities. It may be necessary to use less NFB (i.e. 1.5k) in this design to avoid HF oscillation issues.