Fender Dlx Rev build- last Q b4 fire-up.

[Sea Chief]

Ok 17w is more than enough I'll ever need, and approaching what it says on the tin, so thats ok.

My sanity is being tested with gtr amps like you wouldnt believe.

The gtr sounds pretty good through my wem dominator (ironically a Bass amp) I need only bass & treb at 5 and just use the bright switch- just fine balanced tone (in fact far more playable than this- which depresses me after the time & money its cost compared to that IE x3). This I made/ bought as it had a bass & treb also, so I thoght I could easily turn treb up a bit/ bass down a bit if the sg sounds muddy.. but not as much as Im having to here, and still the bass is prominent with it at 0. The sg sounds like mud too thru my Champ/ I had to add a whopping bright cap to that to make it playable. The sg pickups are f***king sh*t. Im sick and tired of them. An sg should sound bright, snappy its a thin light one-piece gtr which -always- sound bright and zingy on record.. anyway enough of the gtr.

Reverb is right down in the EXT cab/ furthest away. The trem is same as said (nothing audible at all until intensity 5).. but this dud-dud-dud pause dud-dud is slightly maddening me already. And it doesnnt f**k off when trem is pressed off too.

Oh well- thanks so much for helping me anyway.

[Chuck H]

First... Get the pan OUT OF THE EXTENSION CAB. The closer the pan is to the speakers, the worse it will feed back. If it feeds back out of the extension cab then you may have a microphonic tube.

If the trem continues to make noise when switched off there is a miswire. The switch is supposed to stop the oscillator, ergo, no more thud thud thud. So something is amiss. You'll need to trace the circuit to repair it. You may pop a vein in your head but the procedure is just like it sounds. You look at the schematic and then check in the amp to see that what's supposed to be connected is and nothing else.

Did you check voltages for the trem circuit against the schematic? The trem circuit is both triodes of V5.

When I said "17W" it was theoretical based on your assessment of the idle current. The idle current (bias condition) doesn't determine the output power. The amp is very likely capable of about 20W.

A lot of players that use classic Fender designs with humbuckers make alterations to the circuit because of mud. But this should be covered later when the amp is up to snuff. Let's get it working first and then mod it.

[Sea Chief]

A little progress..

Reverb pan out/ well away on shelf nrby head: feedback gone. Not exactly convenient; how a combo fares with it housed below spkr then I dont know.

Nasty buzz on reverb: footswitch pulled and gone. So the reverb circuit itself ok- good. Footswitch does turn trem on/ off but obviously needs seeing to (or not quite the right type?).

Amp background noise normal too now ftsw pulled, but quiet dud-dud-dud pause dud-dud present still (constant speed & -not- same speed as trem). Will check trem circuit today for miswire- altho board gives wire ID to pins/ checked 3x so cant be it. Maybe an added link between pins wrong or jack type or wiring.

And then will check trem circuit voltages with the pdf.

Im going to try the GZ34 back in too- curious of sound difference/ maybe it will give a bit of fender 'zing' Im missing.

[Chuck H]

Reverb pan out/ well away on shelf nrby head: feedback gone. Not exactly convenient; how a combo fares with it housed below spkr then I dont know.

Quieting reverb pans in combos is often a problem and seems to be getting worse with new production pans IME. You may still be able to mount it in the head cabinet as I described before. Noise from the switch cable attachment may be a problem with the shield wiring (or lack of).

but quiet dud-dud-dud pause dud-dud present still (constant speed & -not- same speed as trem). Will check trem circuit today for miswire- altho board gives wire ID to pins/ checked 3x so cant be it. Maybe an added link between pins wrong or jack type or wiring.

A mistake may be non obvious. Check how the cable shield (if present) and leads are connected WRT ground in all switch positions with your DMM.

With the footswitch pulled, the trem is ON. Regardless of background noise, does the dud dud continue with the footswitch connected and the trem OFF? If yes AND it's still a different tempo than the trem the problem isn't the trem, but rather a different low frequency oscillation that may be a consequence of power supply filter problems.

Im going to try the GZ34 back in too- curious of sound difference/ maybe it will give a bit of fender 'zing' Im missing.

That should be fine but with more plate volts the amp should, ideally, be rebiased. With the GZ34 plugged in the tubes will be biased hot WRT the higher plate voltage. Watch for red plating as the amp warms up and during use. This is a condition where the plates of the power tubes can be seen to glow red in dim light (yeah, that's pretty hot!). Any sign of red plating and the amp should be shut down, allowed to cool and then rebiase by INCREASING the amount of negative grid voltage, checking current and doing the subsequent math before continuing.

[Sea Chief]

Yes they are lesser quality than the old accutronics I had in my old £30 s/h PV bandit. I think the pan itslef was £30 korean made alas.

Am going to check trem over & ftsw later- will report findings.

Btw now Ive got the amp back on a normal footing re bias range > plate voltages subsequently down 25V.. what would your pref be. The GZ34 (as the DRRI circuit specifies fwiw) and I guess rebiasing to get the plate V with this down another step (poss ballpark 435V if I were to go more twds the -32V maximum the bias pot allows*).. or the 5U4GB-? would you have had reason to go with a 5U4, if you had found/ fixed the 10k/22k oddity?

[*BTW would this be INCREACING or DECREACING the negative bias voltage-?]

[Chuck H]

WARNING! A brief explanation of bias follows:

It's a balancing act between voltage and current. Since the plate voltage is not typically adjustable we use a circuit that allows us to control the current. This circuit adjust the relationship between the cathode and control grid. For all fixed bias guitar amps the control grid must be maintained negative WRT the cathode. How negative determines the current through the tube when it's just sitting there doing nothing (idle). The more negative the grid, the less current at idle. Ergo, increasing negative voltage on the control grid will decrease current. If we stick to some specific percentage of a tubes rating as a standard for idle bias, higher plate voltage will require lower current and lower plate voltage will require higher current if both are to hold the tube at the same wattage at idle.

In other words, with the higher plate voltage from the GZ34 you will need to increase the negative voltage on the control grid to achieve the same idle wattage you have now with the 5u4.

EDIT: To be clear, it's bad practice to attempt to lower plate voltage by increasing current without consideration of the idle wattage.

The bias arrangement you have now should have the correct range for this without any further modification.

I mentioned before that Hammond, and all guitar amp transformer makers, usually use schematic figures rather than working physical examples for specifications. As it happens there is more than one Fender schematic for the DR. One uses a gz34 and the other a 5u4 but both show the same transformer voltage and the same rectified voltage. It's possible the different era schematics account for changing AC mains voltages here in the US, but that no longer matters because Hammond used the information from the schematic without accounting for this making their rectifier tube spec incorrect. The result is that your power transformer, regardless of any specification, only provides the correct plate voltage with a 5u4 rectifier. Ignore the specifications for the power transformer WRT the rectifier selection. Much more important is the actual operating conditions for the tubes.

[Tom Phillips]

...With the footswitch pulled, the trem is ON...

The Trem is OFF with the foot switch pulled for the Deluxe Reverb circuit.
Tom

[Chuck H]

The Trem is OFF with the foot switch pulled for the Deluxe Reverb circuit.
Tom

You are correct. The last trem I built was a different Fender circuit that defaults to ON with the footswitch unplugged. My bad for not checking this circuit. So...

If the wiring is correct the trem should be off with the footswitch unplugged. With the footswitch unplugged, turn up the intensity control. If the trem doesn't affect the signal then, the rhythmic thud is happening because of something other than the trem circuit.

EDIT: A couple of thoughts... You mentioned a pause in the dud dud dud. That sounded familiar to me. Does the amp do it with the guitar unplugged? Do you have a cell phone in your pocket? If the amp does it with the guitar unplugged try shielding the circuit board with a metal pan lid placed on the open chassis. Does it still do it? Try taking the amp to a different room. Does it still do it?

[guitician]

I had problems with reverb pan feedback in my 50 watt combo and cured it with a vinyl bag that fender used. And be sure to use isolation grommets too.

[Sea Chief]

You are correct. The last trem I built was a different Fender circuit that defaults to ON with the footswitch unplugged. My bad for not checking this circuit. So...

If the wiring is correct the trem should be off with the footswitch unplugged. With the footswitch unplugged, turn up the intensity control. If the trem doesn't affect the signal then, the rhythmic thud is happening because of something other than the trem circuit.

EDIT: A couple of thoughts... You mentioned a pause in the dud dud dud. That sounded familiar to me. Does the amp do it with the guitar unplugged? Do you have a cell phone in your pocket? If the amp does it with the guitar unplugged try shielding the circuit board with a metal pan lid placed on the open chassis. Does it still do it? Try taking the amp to a different room. Does it still do it?

Hi ChuckH- I will re-read your WARNING post for 3rd time later. Still complicated for me. The very idea of negative voltage is like exisstential physics to me, so Im not doing terribly well tbh! appreciated hugely (excellent info for others- sure of that).



Pic shows I hope my decent job.. re the trem circuit wiring- as you can see there's little I can do wrong. Just checked again the wiring is defo fine for V5.

I dont have a cellphone anywhere near (lives in the car as I hate them). I havent tried in a different room, but it is on an extension block with this pc on. Will try with gtr unplugged & with a pan lid over chassis & report back. Will try your suggestions, also do the trem V readings same places I see on the pdf "TP/ Test Points".

[Sea Chief]

I had problems with reverb pan feedback in my 50 watt combo and cured it with a vinyl bag that fender used. And be sure to use isolation grommets too.

Actually Ive housed it in an accutronics bag (proper thick one from my PV bandit) and all is well with it back in the head! result there then.

[Jazz P Bass]

Quote:" Still complicated for me. The very idea of negative voltage is like exisstential physics to me "

Take your digital volt meter & set it to read Volts/dc.
Grab a 9 volt battery.

Hook up the Red lead to the + terminal & the Black lead to the - terminal.
The reading you get will be +9Vdc.

Now, reverse the meter leads.
Black on the + terminal & Red on the - terminal.
The reading you get will be -9Vdc.
(aha! Negative voltage)

Voltage measurements are a matter of reference.

[guitician]

I thought all electrons were negative https://en.wikipedia.org/wiki/Electron

[Sea Chief]

Right a major result.. I put a different tube in V5 (the one I had in thought was a 12AX7 but must have been my only 12AY7.. the info/ numbers rub off these tubes and Ive no idea whats what with a few!).

Trem audible at vol 5, better tone at max/ IE a bit stronger.. but the best thing is the whole amp tone is better: crisper, not flat MUCH better, the highs ping out even with the sg, the low E clear now (was a bit subdued before I couldnt understand why) and the top end too. Now I know what ice-pick highs are! been scratching my head so far.

Voltage at pin 1 of V5 = 350V. Quite a bit high.. pdf states 300V here (the caps are only 400v).

Footswitch now works correctly.

Dud-dud still there but seems only infrequent now (took pc wee transformer thingy further away from plugs)/ easily liveable with.

Reverb hum bad still- but cross that bridge later. Time to play! terrific tone now, just as Id hoped it might be really.

Cant thank you guys enough (esp ChuckH).

[Chuck H]

Hmmm.?...

Nothing about changing V5 should have changed the tone of the amp other than the tremolo function. Not saying it didn't happen. Just saying it shouldn't have.

If the weird duding is reduced by changing proximity to other electronics in the room, that could be the whole problem right there. Does it still happen with the guitar unplugged? Did you try placing a shield over the open chassis? And as a last resort, did you try moving the whole rig into another room? It's probably not the trem making the noise.

Unplug the reverb pan output output from the amps reverb pan input. Meaning, remove the plug from the amp, not the pan. Now turn up the reverb knob. Noisy?