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Post subject: '71 twin, reverb and vib issues and general info
Posted: Sat May 16, 2015 6:38 pm
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Hello, I'm looking for some info about my twin. This is my first tube amp (played acoustic for years, just started shredding). I've been playing it for about a year (love it!) and I feel like I have a good handle on its sound and quarks.

It appears to be a '71: master volume with no push/pull. I believe it's all original. RCA tubes, fender speakers.

The two main issues are
1. The vibrato has always worked, but sometimes it seems more pronounced than others. Also, ticking can be heard when on but not playing (is that just par for the course?)
2. The reverb is on again, off again. Sometimes I fire up the amp and it works...works well, a real puddle of sound. Then it might become less intense, then fade out altogether and then not work. Sometimes I'll fire amp up and it won't work then fade in over time and sound fine. Other times I'll hear a low ringing (moaning kinda) when the reverb is on. Worst when turned up to 10. I can get rid of it by turning reverb down to 1.

Also, I don't really have a frame of reference on my volume. My understanding is that twins are loud as all get out. I certainly hang in there with the band, but my volume settings when playing in a group are such:
Vibrato channel
Volume: 5 (starts breaking up around 7)
Master volume 7 or 8

Is this normal? The guy who plays lead in my band has a fender hot rod deluxe and he keeps his volume at 3 and he's good and loud.

That's where I'm at. Love this amp and I wanna learn about it and I'm game for learning now to fix and update it myself.

Thanks for any advice!

Cheers!

-kay


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Post subject: Re: '71 twin, reverb and vib issues and general info
Posted: Sat May 16, 2015 7:19 pm
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Hi PantherHeart,

Sounds like you are due for a thorough checkup, possibly new filter caps, and maybe new tubes. You could have problems with your sockets, jacks and pots, they all might need to be cleaned.

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Post subject: Re: '71 twin, reverb and vib issues and general info
Posted: Sun May 17, 2015 12:50 am
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shimmilou wrote:
Sounds like you are due for a thorough checkup, possibly new filter caps, and maybe new tubes. You could have problems with your sockets, jacks and pots, they all might need to be cleaned.


+1

That's how I'd proceed. Once the basic "housekeeping chores" have been addressed, any lingering symptoms can be isolated and diagnosed individually as required. The amp's nearly forty-five years old -- it's bound to need some maintenance and servicing.

Arjay

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Post subject: Re: '71 twin, reverb and vib issues and general info
Posted: Sun May 17, 2015 4:14 pm
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The vibrato tick is normal. There are mods to improve it. It may need a new optoisolator for best performance.
Vibrato is kinda funny, in that some speeds are more noticeable than others. If its very unstable, cleaning the Depth pot may be in order.
I think its unlikely to be a tube. That would either crackle or just quit and not come back.

As far as the reverb goes, check the RCA connectors on the back They should be tightened for stable operation. Squeeze the ears closer for a tighter fit.
If you're using a reverb footswitch, that could be part of the problem. It's used to ground out the reverb signal and if its cable is damaged or the switch is going bad, it can cause strange problems.
Try unplugging the footswitch when it acts up and see if that doesn't improve it.

Your particular Twin has a very low internal gain. These low dynamics give a lot of clean headroom for rhythm guitar. It also allows you to jump up n down on the strings without clipping.
The HRDX is much higher internal gain and a light touch is needed to control its gain.
The differences you describe are normal.


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Post subject: Re: '71 twin, reverb and vib issues and general info
Posted: Sun May 17, 2015 9:00 pm
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TimsAudio wrote:
If you're using a reverb footswitch, that could be part of the problem.


I pulled the footswitch and the reverb came right back, and sounded clean. Then I thought I might just leave the connector for the reverb out and the vib in, set my reverb to 3 and have on/off control with my vib. No such luck though: vib only works with both connectors plugged in.

Later, with the foot switch fully plugged in, I did have the reverb, but the warbling ringing as well. When I went to flip the standby switch, I hit the top of the amp and effected the warble. So I cranked up the reverb to 10 to get max warble and started tapping lightly on the top of the amp and made the warble get better then worse then awful sounding. i think I will have a pro give it a once over.

Thanks for your thoughts and advice everybody.


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Post subject: Re: '71 twin, reverb and vib issues and general info
Posted: Sun May 17, 2015 10:24 pm
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PantherHeart wrote:
So I cranked up the reverb to 10 to get max warble and started tapping lightly on the top of the amp and made the warble get better then worse then awful sounding. i think I will have a pro give it a once over.


You have a microphonic component (tube, coupling cap, cathode resistor, etc) or a marginal solder joint.

Arjay

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