It is currently Mon Mar 16, 2020 10:50 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 12 posts ] 
Author Message
Post subject: '67 DR Reverb Hum
Posted: Sat Aug 13, 2016 9:43 pm
Offline
Hobbyist
Hobbyist

Joined: Sat Aug 13, 2016 9:17 pm
Posts: 3
Hey, all:

I've been researching on a number of forums, but still no luck, so thought I'd post with my specific symptoms. I have a 67 (maybe 68?) blackface Deluxe Reverb that I'm restoring. I'm down to the last piece: the foot switch. Everything was fine until I plugged it in, and clicked on the reverb. I get a nasty 60-cycle hum. It gets louder as I crank the reverb up. If I hit the switch to turn off reverb, hum goes away. If I unplug the footswitch entirely, and play through the vibrato channel with reverb turned up, there is very minimal hum, but it follows the volume knob; I can keep volume down and crank reverb way up, and no hum. What I've tried so far:

    * Rotated the reverb tank to orient the RCA connectors to the back of the amp (yeah, I know... I saw it mentioned in another forum, and I was skeptical, but it was an easy test, and now, at least, I can read which is 'in' and which is 'out' on the tank). -> No change.
    * Grounded the reverb tank housing -> No change.
    * Noticed that the footswitch housing was not grounded, so I grounded it by soldering a lead from the reverb switch pin connected to the wire shield to the inside of the metal switch enclosure. -> No change.
    * Cleaned the RCA connectors on the chassis with steel wool (the cable and tank are brand new, so the connectors are very clean). -> No change.
    * Cleaned the points of the 12AT7 tube (3rd from right) -> No change.
    * I have a 7024 in the 4th position from the right (ran out of 12AX7s; but I read the two are interchangable). Cleaned the pins for this tube as well. -> No change.
    * Some time ago, I added a three-pronged power cord (amp came without). I wired the + and - leads to their original places, and screwed the ground lead into the chassis.

I can't help but think that since the problem follows the switch, there's something there, but it's brand new, I compared the wiring to a couple diagrams of the same I located, and put a meter to it looking for any shorts, and it seems to be clean. Any thoughts on what I might also try are really appreciated. I'm in the homestretch on this and really anxious to get it fully functional again.

Thanks,
Rich


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: '67 DR Reverb Hum
Posted: Sat Aug 13, 2016 10:17 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26416
Location: Tombstone Territory
Rich66 wrote:
(the cable and tank are brand new, so the connectors are very clean)


Are you certain that the tank is the correct type for your amp?

There are a couple of different grounding schemes that a tank may use and these methods are not interchangeable. As well, input and output impedances vary by application and may cause the reverb circuit to hum if these parameters are not matched to the amp. IIRC the vintage Fender tanks (Hammond or Belton) are internally grounded and should show a DCR measurement of 0.81Ω at the input and 82Ω at the output. Check your tank carefully.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Sun Aug 14, 2016 2:11 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14047
Location: Province de Québec, Canada
1-Bad wired lead dress inside the amp ; show some pictures.
2-Wrong reverb tank.
3-Bad shielded wires from amp to the tank, try new one, any home stereo wires work.
4- Dirty or loose tubes socket.
5- Noisy reverb tubes

Never use steel wool to clean socket or connector or any electronic contact ; you remove the protective coat. You may have some problem in few months with these contacts.


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Sun Aug 14, 2016 10:44 am
Offline
Hobbyist
Hobbyist

Joined: Sat Aug 13, 2016 9:17 pm
Posts: 3
Quote:
There are a couple of different grounding schemes that a tank may use and these methods are not interchangeable. As well, input and output impedances vary by application and may cause the reverb circuit to hum if these parameters are not matched to the amp. IIRC the vintage Fender tanks (Hammond or Belton) are internally grounded and should show a DCR measurement of 0.81Ω at the input and 82Ω at the output. Check your tank carefully.


I picked up a 4AB3C1B. Problem is, it seems difficult to find a definitive (i.e., from Fender) indication of what the "correct" tank is. I ordered this from an online retailer that listed this specific model as being used in the vintage DRs, and it matches the replacement tank in the Fender store, with the exception of the last character (Fender's is vertical mount, the 4AB3C1B is intended for horizontal mounting). So with all that, I believe I have the correct tank (but always open to better evidence).

I verified that the output is connected to ground, as per the spec (input insulated/output grounded) from Accutronics. The stated values from Accutronics are 500Ω on the output, and 8Ω on the input. Perhaps I'm measuring incorrectly, but I'm seeing ~255Ω on the output, and ~2.6 on the input (measuring resistance from tip to ring on output, and then tip to ring on input).

1 - Not sure what you're looking for here - cold solder joint somewhere, perhaps?
2 - See above
3 - I performed open and short testing on the RCA cables from the chassis to the tank, and they came back clean. Cables were new, also, but worth testing to rule out manufacturer defects.
4 - Haven't tested and not really sure how, other than resoldering the leads...
5 - I swapped V3 with a spare 12AT7 -> no change. I also swapped V4 and V1 tubes. Since the buzz did not follow the tube over to the normal channel, and persisted on the vibrato channel, I think that the tubes can be eliminated as a cause.

Seems like I have exhausted all my attempts at not pulling out the chassis, so that's my next plan of attack. That said, any comments on the extent to which a relatively clean signal without the switch, vs. a buzz with the switch might imply a switch or switch cabling problem?

Thanks,
Rich


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Sun Aug 14, 2016 11:42 am
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Fri Aug 21, 2009 1:45 pm
Posts: 852
Location: SoCal323
When you unplugged the switch the problem went away, correct? Or at least the hum was minimized to an acceptable level? Minimal hum is normal when the foot switch is unplugged. Better cables and a quiet 12at7/12ax7 will help bring it down. It's not unheard of to have a footswitch introduce the issue you've described. I'd try to source a viintage/original footswitch and see if the problem still occurs. Another thing, is the problem still there if you unplug the reverb cables but plug in the foot switch?

Hope this helps.

_________________
Its a lifestyle.....

Image


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Sun Aug 14, 2016 12:10 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14047
Location: Province de Québec, Canada
4AB3C1B must be the right one
I read 245 and 1.1 ohms on mine, yours look good.

You don't need a switch to power ON the reverb, reverb is alway ON.
You need switch only for tremolo
If you have hum only with pedal switch plugged, look at the pedal switch.

What about some pictures ?


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Mon Aug 15, 2016 5:25 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Rich66 wrote:
Hey, all: I get a nasty 60-cycle hum. It gets louder as I crank the reverb up. If I hit the switch to turn off reverb, hum goes away. If I unplug the footswitch entirely, and play through the vibrato channel with reverb turned up, there is very minimal hum, but it follows the volume knob; I can keep volume down and crank reverb way up, and no hum.
Thanks,
Rich


You sure you didn't accidentally have the vibrato side of foot-switch plugged into the reverb RCA jacks?


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Mon Aug 15, 2016 6:00 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26416
Location: Tombstone Territory
BMW2002Ti wrote:
You sure you didn't accidentally have the vibrato side of foot-switch plugged into the reverb RCA jacks?


+1

This is the correct configuration for the footswitch cables......

Image

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Mon Aug 15, 2016 9:15 pm
Offline
Hobbyist
Hobbyist

Joined: Sat Aug 13, 2016 9:17 pm
Posts: 3
I double checked, and the reverb switch is connected to the reverb switch receptacle, and the vibrato is connected to the vibrato receptacle (good thought, tho).

Here's a chart of the different states of cables/connectors affect the noise. (Sorry for the lack of alignment... Thought the code tag would produce a monospaced font...)For this chart:
* RVB Connector and VIB Connector refer to the RCA plugs coming from the respective switches.
* RVB Tank indicates whether *both* cables are connected or disconnected.
* Noise refers to "unreasonable noise". As I mentioned earlier, there is always some amount of noise, particularly when the reverb switch is disconnected, but it's not what I would call unreasonable.

Code:
RVB                       VIB
Connector     RVB Switch  Connector     VIB Switch  RVB Tank     Noise?
------------  ----------  ------------  ----------  ------------ ------
Connected         On      Connected         On      Connected      Y
Connected         On      Connected         On      Disconnected   Y
Connected         On      Connected         Off     Connected      Y
Connected         On      Connected         Off     Disconnected   Y
Connected         On      Disconnected      N/A     Connected      Y
Connected         On      Disconnected      N/A     Disconnected   Y
Connected         Off     Connected         On      Connected      Y
Connected         Off     Connected         On      Disconnected   Y
Connected         Off     Connected         Off     Connected      Y
Connected         Off     Connected         Off     Disconnected   Y
Connected         Off     Disconnected      N/A     Connected      Y
Connected         Off     Disconnected      N/A     Disconnected   Y
Disconnected      N/A     Connected         On      Connected      N
Disconnected      N/A     Connected         On      Disconnected   N
Disconnected      N/A     Connected         Off     Connected      N
Disconnected      N/A     Connected         Off     Disconnected   N
Disconnected      N/A     Disconnected      N/A     Connected      N
Disconnected      N/A     Disconnected      N/A     Disconnected   N


Here's the wiring of the switch:
Image

One of the things I found interesting in this wiring is that if you pull the reverb connector, you lose vibrato, too, since the vibrato switch leverages the shielded lead of the reverb wire to complete its circuit. Seemed an odd way to wire that, but I haven't been able to find any images of vintage switches wired differently, so assuming that's correct.


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Mon Aug 15, 2016 10:15 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26416
Location: Tombstone Territory
Vintage footswitches are wired in precisely the same manner. However, it is imperative that the ground wire attached to the interior of the housing be solidly soldered. I've had to re-heat that joint on several repro switches, you might try the same. Forget the 40-watt pencil -- you need a 100-watt industrial iron to produce sufficient heat.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Mon Aug 15, 2016 10:39 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Something doesn't look right about that wiring. You may need to do a continuity test and check the switch actions against the schematic. Here's photo of OEM unit.

Image


Schematic.

http://ampwares.com/schematics/deluxereverb_ab868.pdf

Ground solders are critical to avoid loops (and associated hum). Measure resistance between ground solder points on footswitch and chassis with RCA wires connected. Should be close to zero ohms, with switches in proper positions.

Should be shielded cable.


Top
Profile
Post subject: Re: '67 DR Reverb Hum
Posted: Tue Aug 16, 2016 2:18 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14047
Location: Province de Québec, Canada
There is no shield wire on your pedal switch; that is why you have some noise


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: