65 deluxe reverb reissue

[Rockranger]

Found a guy who gutted a new deluxe reverb reissue to do a hand wired version of it, so I got the pots pcb, the main pcb and the caps pcb for next to nothing and decided to try to put a cheap version of this amp together. So I bought the transformers, tube sockets, tubes, optoisolator and built a chassis and slapped it together. The amp is working but I have a few problems, I put in a bias testing spot and my bias is reading from 0 to 10 mv (the optimal reading for this amp is 25). You can hear my optiosolator loudly pulsing through the speaker when reverb and vibrato is engaged even with all the knobs at 0. Obviously with bias numbers out of whack the amp sounds pretty bad, with only a couple of kits under my belt mabey I'm in over my head with this one any ideas would be greatly appreciated! I rented this amp at a local dealer and pulled it apart to make sure mine was put together properly and I couldn't find any differences. Everything that I bought that I listed above was a direct replacement for this amp ( the transformers are Hammond). My plate voltage sweeps from 440 VDC to 462 with the bias adjustment (420 is supposed to be ideal).

Thanks

Thanks

[92Volts]

Bias is controlled by a negative voltage, which (like all voltages in the amp) is derived from the power transformer.

Assuming yours matches this schematic: http://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-65-Deluxe-Reverb-Schematic.pdf
... the power transformer has a separate tap devoted to the bias supply (the red/blue wire). In other designs negative voltage is derived from the main power winding.

Anyways, if your transformer doesn't match Fender's very closely you could end up with too much negative voltage, and too little current through the tubes.

Test point 5 is what we're talking about here, it should be -49 volts. Test point 36 is supposed to be -37 volts but should be somewhat adjustable using the variable resistor R58. Because you have higher plate voltage, you might need bias voltage (at TP36) SLIGHTLY lower (more negative) than the schematic says, but not too much.

Without major changes you can't "fix" the voltage at Test point 5 but by swapping just 1 or 2 resistors, you can adjust the portion that goes to the tubes (measured at TP36). Check those voltages before planning any tweaks, though.

[bnwitt]

I hate to say this but all that stuff you got for next to nothing is worth next to nothing.  All the other stuff you bought just got married to junk.  There's a reason we rip that crap out and through it away.

[Rockranger]

Thanks for the feedback guys, you were right test point 5 is -68 and test point 36 is -45. So do you think I'm looking at having to get a new PT to get this thing working properly?

[92Volts]

It sounds like you've tried adjusting R58 to change the bias, what effect does this have on available voltage at TP36?

Based on the values of R58 (the bias adjust pot) and R59, it should provide a range from (the voltage at TP5) to (1/2 the voltage at TP5). This "should" get you as high as -34v which "should" be high enough. Each set of tubes is different so you might need higher voltage than what's available now but still, you should be able to get TP36 higher than -45 volts.

Lowering R59 will give you a wider range of adjustment (let you bring it closer to zero) if needed.

[Rockranger]

Thanks for the help 92volts, my bias bias adjustment swings test point 36 from -70 volts to -45 volts. How much would you suggest lowering R59? do you think that will get me where I need to be?

[92Volts]

I think changing it from 10k to 5k would be reasonable. Make sure to set the adjustment back to a low setting before running the amp with tubes in it!

It's not a bad idea to check the resistance of R59 and R58 (across the two ends) if you have a multimeter, and/or by reading color codes on R59. When they're in the circuit, surrounding components sometimes affect the multimeter result, but once R59 is removed you should be able to read R58 without removing it.

One of those is not exactly as described on the schematic. All components have a tolerance, R58's is probably as big as +/-20%, but it's still worth making sure they were the right components in the first place and are in the right ballpark.

[Rockranger]

You were right on the money again r59 was actually a 22k resistor instead of the 10k shown on the schematic, i replaced it with the 10k and I have a nice range on my bias pot, the only thing now is I get a high pitched squeal when I go above 15mv on my bias. Seems like most people set it between 20 and 25 from what I've seen, and even before 15 it is much noisier!

[sluckey]

Swap the OT primary plate leads. Does that help the squeal?

[Rockranger]

Switching the OT did the trick, really appreciate all the help guys the amp sounds fantastic on the normal channel. The only thing I have left to figure out now is the pulsing sound from the optoisolator coming through when the reverb/vibrato is engaged, it is brand new and was the only thing missing from the board when I got it. The optoisolator was genuine fender part that is supposed to be good for all fender vibrato amps?

Thanks again

[92Volts]

Glad you got the bias fixed!

Does R48 (intensity) knob effect the noise coming through? Also, you say it's coming "from" the optoisolator, but many other parts are involved in the vibrato. Was the noise not present until you reinstalled the optoisolator?

[sluckey]

The AB763 amps require a shielded cable for the reverb but not for the tremolo. Are you using a proper footswitch? And is the jack wired properly? If you just unplug the footswitch does the reverb sound OK. (Trem will not work with footswitch unplugged.)

[Rockranger]

92 volts I'm not exactly sure that it is optoisolator the sound of the light flashing in the optoisolator is what I'm hearing.
Sluckey I am not using a proper foot switch so that could be it I am just using a always on jack which is just a jack with the tip wired to the shield. The reverb is working properly but it brings a lot of noise to the amp. The vibrato channel in general is much more noisy than the normal channel!
I won't get a chance to take a good look at this for a couple of days because I' on a stretch of shift work, thanks for all the help and hopefully I'll be able to provide more info then!

[sluckey]

If you just unplug the footswitch does the reverb sound OK?

[Rockranger]

Yeah the reverb works properly with foot switch unplugged.

[sluckey]

Yeah the reverb works properly with foot switch unplugged.

OK

I am just using a always on jack which is just a jack with the tip wired to the shield.

What is an "always on jack"? The shield should connect to the sleeve, not the tip.

If you see the opticoupler bug flashing then there's not much more that could be killing the tremolo. Just the other half of the bug or the INT pot or the wiring. Look at the schematic. Should be an easy fix.

[Rockranger]

Yeah for sure, I should be able to finish it off when I get to put some time in on it, thanks for everything guys! I'll post a pic when it's done.

[SILVERGUN]

What is an "always on jack"?

https://reverb.com/item/905334-always-on-plug-for-fender-65-deluxe-reverb-reissue-replaces-footswitch

[sluckey]

What is an "always on jack"? The shield should connect to the sleeve, not the tip.

Ah, I see. Talking about a plug, not a jack.