Fender Blues Deluxe Reissue

[bsco]

I have a Fender Blues Deluxe Reissue and I can''t seem to obtain the correct schematic. The only schematic I can find on the Fender (and other sites) is for a Blues Deluxe which has fixed bias. The Reissue model has an adjustable bias pot. Anybody know what the bias setting is supposed to be and does anybody have a schematic for the bias circuit?? Thanks very much...
Bernie

[52 Bill]

Anybody know what the bias setting is supposed to be and does anybody have a schematic for the bias circuit?? Thanks very much...
Bernie

If you look at the left side of tube socket board you should see a 1 ohm resistor, R66. One side is grounded and the other end connects to the output tube cathodes. Read the dc voltage across R66 and set the trimpot for a reading of 60mV. No signal and the tubes should be warmed up.

[Jazz P Bass]

Fender Blues Deluxe RI Schematic

Here is the schematic.
52 Bill is correct.

[bsco]

Thanks very much for your help.Checked out the bias setting. There is no bias voltage at all..even when the pot is rotated throughout it's entire range. Now that I have the proper schematic hopefully I can figure this out. I'll post my findings once I have a look. Thanks to both of you for your help....

[52 Bill]

There is no bias voltage at all..even when the pot is rotated throughout it's entire range.

Do you mean that there is no reading across the resistor R66, or that there is no negative bias supply voltage?

If you mean there is no reading across R66, then check the diode that is in parallel with R66 and check R66 as well. If either one is shorted there will be no reading there.

If you mean that the bias supply voltage is missing, then check the power supply diode and the fliter cap for shorts.

[bsco]

I meant to say that there is no reading across R66. The bias pot can be adjusted from -76 volts to approx - 104 volts. So I guess that the bias pot and power supply should be ok. I will have to disconnect on end of R66 in order to check the diode for a short seeing as the resistor is only 1 ohm... It is getting late so I will have another run at this tomorrow and after our snow storm is over tomorrow afternoon, I can have the luxury of shovelling snow. Thank you very much for your suggestions. I'll let you know what I find tomorrow.....

[Enzo]

-104 volts????????

Where are you grounding your meter, and are you measuring at pin 5 of the power tubes?

If you really have 70-100v of bias voltage, then I don;t doubt you have zero tube current at the test point. But the raw voltage the bias dervices from ought to be only -53v to start with.

[bsco]

Hi Enzo. I checked out what you suggested. The voltage at Pin 5 on both power tubes can be varied from -74 to -104 volts
by varing the bias pot through it's entire range. THis is the same voltage as measured from the wiper connection of the bias pot as well. I am using chassis ground. Can't see any overheated, burnt components or any broken solder connections/traces and nothing seems to be overheating at this point.

[bsco]

Had another look at my problem..did some checking for broken traces. Everything ok there. I did notice something. According to the schematic the deluxe is supposed to have C37 omitted and D10 omitted and a jumper J2 inserted. These parts are supposed to be stuffed in the Deville. Inside the back cabinet the label states that it is a Fender Blues Deluxe Reissue and therefore these parts are not supposed to be there. As it stands now I have -53 volts on the cathode end of D10 and the higher voltage on the anode end. I then removed C37 and it is rated for 47 uf at 160 volts. Has anybody seen this type of a difference before??

[Enzo]

Look at the two power supply versions, the Deluxe and DeVille. The difference is the transformer. The small parts change because the transformer feeding them changes. Ther are a bunch of these amps that are sort of transitional. Yes, I see it a lot. And note the schematic says parts such and such are not stuffed on Blues De ville pc board assembly. That isn't exactly the same as the Blues DeVille AMP.

The higher voltage cap was a change either for inventory reasons or they increased the voltage on it for reliability reasons somewhere along the production run.

But you provided the clue. Whichever version you have, the cathode of D10 should be at ground. SO how can it have -53v to ground. FInd out why it is not grounded. And verify the transformer wires are on the correct posts. DOn;t remove the parts until you know what is going on in there.

WHat part number transformer do you have?

[Enzo]

Is the ground wire from the end of the board screwed to the chassis at this time?

[bsco]

Hi Enzo. Bernie here. Sorry about that last post. I made a mistake. Here is what I have...The cathode end of D15 measures approx -52V..the anode of D15 measures -104V approx. The cathode of D10 is 0v and the anode of D10 is the same as D15...-52V R78/79 have +47/-47 on one side and +/-16V on the other sides. The bias pot was rotated to center and the voltage measured at the junction of the pot and R76 is -73V..The other end of the pot has approx -104V and the wiper connection has approx -77V..When you adj the bias pot the voltage on Pin 5 of both output tubes will vary from approx from -52V all the way up to -104V... Sorry about the confusion with the last post. Thw main ckt board is grounded with a heavy duty jumper wire and is secured to the chassis as I checked it for continunitity... The part number of the transformer appears to be the one for the Deluxe...B-036958.....there are a bunch of other numbers there but none of them match the part numbers for either transformer.

[g1]

Those readings are strange. Your pin 5 voltages should be pretty much the same as the voltage at the wiper of the bias pot.
Also, you are saying that the voltage at the junction of D15/R76 is -52V but at the junction of R76/bias pot you say it is -73V. I don't see how this is possible.
Was the amp working ok, was there a fault or are you just wanting to set the bias?

P.S. On a side note, if anyone would care to explain C37 in the top bias supply drawing, it would be appreciated.

[bsco]

Actually, the voltages at Pin 5 of both tubes are the same as the wiper voltage at the bias pot. I am sorry for that confusion. What I had actually meant was that the voltage at Pin 5 would change in step with the voltage at the wiper of the bias pot...so whatever voltage was at the wiper pin, that was the voltage at Pin 5. The amp came in with a badly distorted sound and you have to crank the volumes up on full to get anything out of it. When I went to measure the bias voltage at the test point, there was none. Checked the traces,, the 1 ohm 1W resistor and diode and was good. I guess the tubes are completely cut-off and only the very peaks of the audio signal are strong enough to push some of the sound through the spkr but very very badly distorted...

[bsco]

How about this..I take out the two output tubes and run a signal to the input jack and scope the pre-amp out to see what is there?? THat will tell me if i have other problems I guess..