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Post subject: Deluxe Reverb Build Help
Posted: Mon Apr 10, 2017 4:35 pm
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Roadie
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A couple of weeks ago I built a Deluxe Reverb in a tweed chassis using a multi can 40/20/20/20 to save room. I've done many (20+) Fender style builds, tweed and blackface and have done my share of repairs for locals as well. That being said, I'm not a rookie but by no means an expert. Regretfully, I do not have an O scope.

This amp has had a loud 60 cycle hum from the beginning. It gets quieter with the volume at 6 but it's loud at 0 and 12. The volume seems lower than it should be as well. It stops completely if I pull the PI tube. I've gone through the schematic and layout at least 5 times to confirm everything and have already done the following:

-checked all voltages (many times)
-new tubes
-pulled the board, built and installed another new one with all new parts, all new wiring, etc.
-replaced everything on the bias board
-new bias pot
-new reverb trans.
-new choke
-built an out of chassis standard Fender filter cap board with all new caps and resistors, grounded of course
-rearranged the grounding scheme, tried star grounding, etc.
-disconnected the tremolo circuit
-tried shielded/grounded on one end of the input leads
-made sure the heater wires were parallel

Basically the only thing I haven't changed are the PT, OT, tube sockets and pots. All the voltages are good/within reason including B+1, 2, 3 and 4. It biases fine, no fluctuation in pv.

Just wondering if anyone might have some advice. I posted a YouTube link, hopefully that will give a decent idea of what it's up to. Maybe just to much circuit crammed into a small area.

Thanks, GW

Image

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Post subject: Re: Deluxe Reverb Build Help
Posted: Mon Apr 10, 2017 5:38 pm
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My first thought is, where is the ground of the cap can connected?

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Post subject: Re: Deluxe Reverb Build Help
Posted: Mon Apr 10, 2017 5:47 pm
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Hi Shimmilou, it's been a while. I had 2 of the tabs grounded directly to the chassis via a wire. I removed one, it should only need one good ground for the whole can. I did try a regular filter board outside the chassis as well with no change.

GW


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Post subject: Re: Deluxe Reverb Build Help
Posted: Mon Apr 10, 2017 8:14 pm
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You sure it's a 60Hz hum and not 120Hz? It'll make a difference how you track down the hum. 60Hz is below lowest open E-string, standard tuning. 120Hz is around open A-string.

60Hz hum is prolly heater line. Or something before the rectifier. 120Hz is usually PSU related (after the rectifier). Ground loops usually involve the grounding loops between the PSU and input sections of the amp.

If the hum comes on, after warm-up... clean the rectifier tube's contact with the socket. Also, output tube sockets.

Output tubes are biased within normal range?

BTW... very nice DIY wiring! Neat and clean. :mrgreen:


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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 6:03 am
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To my ears it sounds like 60 but I'll check into it more. I can rewire the heater line again with new wire, maybe try it away from the chassis above the sockets, just to see.

I gave some thought to trying a bus ground that would include the reverb and tremolo jacks.

The sockets are all new Belton but I'll give them a cleaning anyway.

Tubes are biased fine, actually even a touch cold.

I'll try going straight to on, bypassing stby and see if the hum is parallel to warm up.

Thanks for the info, I appreciate any help with this. GW


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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 6:36 am
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2- Heaters center tap are well grounded ?

3- Wrong forum ; this is not a Vintage Guitar Amp, it is a Modern Guitar amplifier ( 1985 current ) amps :lol:


Last edited by stratele52 on Tue Apr 11, 2017 8:01 am, edited 1 time in total.

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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 6:59 am
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Diode - the voltage is negative.

I posted here because the circuit is before 1985.

There's no CT on this Classic Tone PT for the heaters. I'll try an artificial CT with 100 ohm resistors.


Image


Last edited by upnorth2 on Tue Apr 11, 2017 7:17 am, edited 1 time in total.

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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 7:12 am
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stratele52 wrote:
1- Picture show diode on bias circuit are reverse :oops:

2- Heaters center tap are well grounded ?

3- Wrong forum ; this is not a Vintage Guitar Amp, it is a Modern Guitar amplifier ( 1985 current ) amps :lol:


Stratele... bias supply diode should have striped end pointing toward drop-down resistor. Toward the PT tap for the bias supply. No?

http://i894.photobucket.com/albums/ac14 ... 6cuppw.jpg

Like this?

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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 8:03 am
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[quote="upnorth2"]Diode - the voltage is negative.

I'll try an artificial CT with 100 ohm resistors.


/quote]

Yes negative, I did not look carefully the circuit :oops:
Ok if you do an artificial CT, many people forget that


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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 12:25 pm
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You guys brought up the heater wires and CT. I added the following:


Image


and it solved the problem!! Thank You.

Sometimes the simple things get overlooked the easiest. Just a slight hiss now that I'll be able to clean up now that my ambition level with this amp has been rekindled. The Jupiter's and Sozo's need to go back in now along with a few other things. I'll post some finished pictures, almost turned the cab into a low power tweed Twin with a single 12" project.

Thanks again men, GW


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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 1:14 pm
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Glad the build is now back on track!

Arjay

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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 1:35 pm
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Heaters need always a center tap to ground :)

I see so many low budget vintage amps with no ct.

Enjoy.


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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 7:51 pm
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upnorth2, what you are doing is setting an artificial CT to ground --- when the tranny did not have an actual wire CT for the heater taps. The 100-ohm resistors also raises the potential voltage above 0. This helps reduce the AC hum transfer from heater lines to cathode, in the tubes.

Valve Wizard explains it more eloquently. :mrgreen:

http://www.valvewizard.co.uk/heater.html


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Post subject: Re: Deluxe Reverb Build Help
Posted: Tue Apr 11, 2017 8:23 pm
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Some good info on that site BMW2002Ti. I've added artificial center taps to amps before. I should have realized the need for it if there wasn't one on the PT heater tap. Mistakes like this end in egg on one's face.

UN


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Post subject: Re: Deluxe Reverb Build Help
Posted: Wed Apr 12, 2017 1:45 am
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Where did yo find the layout to built a Deluxe Reverb with no heater CT ?

I never see a DR schematic with no heater CT on power transformer.


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