Have you measured all of the nodes of the B+ rail? A lower plate voltage on your 6L6s will cause colder bias for a given neg. bias voltage. I would check the supply nodes and the corresponding plate voltage directly at the pins of the tubes. This will also help to find bad resistors if the voltages seem way off. Also check the bias voltage on pin 5 of the 6L6s for -50 volts or so and the raw bias voltage of around -74v where diode 15, C43 and R76 connect. Make sure your B+ is correct first, then repair things. Around 485v on the rail, around 480v on the plates, 2 or 3 volts less for each on the screens,etc.
Yes, thanks that all makes good sense. There is about -50 on the output tube grids.
I powered it up and tapped around and found that it made the sort of crackling sounds when I tapped the input jacks. Tilted the board back and I'm going to fix the cracked solder joints there first. My son said that he thought that the speaker vibration was hitting the jacks and causing the cracking. He probably knew that if he tapped on the input plug it made the sound.
Interesting that the "mod" had no signs at all of being a mod, solder pads looked exactly like all the others with no flux or any sign that it was new.
Could this have been factory work?
I'm really temped to put small 10 ohm resistors in series with the output cathodes to burn up if it red plates again.
I powered it up and tapped around and found that it made the sort of crackling sounds when I tapped the input jacks. Tilted the board back and I'm going to fix the cracked solder joints there first. My son said that he thought that the speaker vibration was hitting the jacks and causing the cracking. He probably knew that if he tapped on the input plug it made the sound.
Interesting that the "mod" had no signs at all of being a mod, solder pads looked exactly like all the others with no flux or any sign that it was new.
Could this have been factory work?
I'm really temped to put small 10 ohm resistors in series with the output cathodes to burn up if it red plates again.
If whoever did the mods was really good, it could look like factory work. It can be done.
Were the 6L6s redplating when TP 30 read 25mV? It seems quite a ways to go from such a cold bias,12.5mA per tube, to redplating. Have you made the plate and screen voltage measurements? It seems as though something there has to be off. The jack input crackling shouldn't have anything to do with this. How about the cathode resistor? Does it measure 1 ohm? Also the screen resistors-470 ohms? For the voltage measurements at the tubes, you should be able to reach the pins of the power tubes as they are elevated from the circuit board. The tubes are held up off the board by standoffs. Good thing you are comfortable doing this with power on!
By all means, solder in that input jack so you can access the #1 input.
Since that 1 ohm resistor handles both tube's current, do you think it will burn up if the tubes start to redplate. If you keep a close eye on them and shut it down right away, redplating shouldn't hurt it. You have a little time, unless of course they turn bright red. And you tested the tubes, including for shorts, not just emission or transconductance?
Were the 6L6s redplating when TP 30 read 25mV? It seems quite a ways to go from such a cold bias,12.5mA per tube, to redplating. Have you made the plate and screen voltage measurements? It seems as though something there has to be off. The jack input crackling shouldn't have anything to do with this. How about the cathode resistor? Does it measure 1 ohm? Also the screen resistors-470 ohms? For the voltage measurements at the tubes, you should be able to reach the pins of the power tubes as they are elevated from the circuit board. The tubes are held up off the board by standoffs. Good thing you are comfortable doing this with power on!
By all means, solder in that input jack so you can access the #1 input.
Since that 1 ohm resistor handles both tube's current, do you think it will burn up if the tubes start to redplate. If you keep a close eye on them and shut it down right away, redplating shouldn't hurt it. You have a little time, unless of course they turn bright red. And you tested the tubes, including for shorts, not just emission or transconductance?
Last edited:
I just called Fender, 800 856-9801 and chose get more information on your amp, sounded like a dead end then after less than a minute a person came on who could speak English and understood exactly what I was asking. Informed me that per our serial number it was made in November of 2001. I mentioned the mod and he said it is possible that it was a factory mod and looked for more schematics. He asked about the revisions in the upper right corner of the schematic that I was looking at and I told him Released PR323, he said he had PR 247 and I told him that, that was the type number on the back of the unit. He emailed it.
It is the Blues Deville schematic and does not match. He said that he wasn't sure if it would match and I emailed him back to see if he could find something better.
Anyone know what exactly these PR designations mean? Makes no sense that the PR247 matches but not the schematic.
It is the Blues Deville schematic and does not match. He said that he wasn't sure if it would match and I emailed him back to see if he could find something better.
Anyone know what exactly these PR designations mean? Makes no sense that the PR247 matches but not the schematic.
PR means "product release" and refers to the engineering project that produced the project. In the trade we do not use that number for warranty claims etc, we use the model number. Changes occur during production, up to and including complete rework of the circuit board. For example The original 1995 Hot Rod deluxe and Hot Rod DeVilles were separate boards, and each also had revisions, but the 2001 version made a common board shared by the two models. Differences in parts stuffing made which model the board was. regardless of board, the HR Deluxe was PR246 and the HR DeVille was PR247. But those same PR numbers referred also to the original Blues Deluxe and Blues DeVille models. PR323 appears to be a later project number for the reworked circuit and board.
The service file is too large to post in this forum. So I posted it elsewhere for you. Look here if you are interested:
Fender Hot Rod DeVille file
The service file is too large to post in this forum. So I posted it elsewhere for you. Look here if you are interested:
Fender Hot Rod DeVille file
Any progress on those voltage readings? The schematic you posted is the correct one, or very close. It still would be a good idea to get the B+ rail and the corresponding readings at the pins of the tubes. You will be taking those readings talked about in post # 21,#23 sooner or later. I have owned this model amp since 1998 and know it very well. Mine is a PR 247 amp. All I have seen is that you have -50v bias. This helps but without knowing the plate,screen and preamp plate voltages you won't know what is working properly and what is not.
My first link was to a very good forum for guitar amps, a lot of very knowledgable and helpful people. Unfortunately I forgot there was a problem with certain files due to a server crash we had. DIY is a great forum, but mainly about hifi. Anyone serious about tube guitar amps ought to visit the MEF as well.
The second link is to a solid state guitar amp forum, also worth a visit, but maybe not as helpful for tube amps.
The second link is to a solid state guitar amp forum, also worth a visit, but maybe not as helpful for tube amps.
Thanks very much Enzo.
That manual has several versions of the schematics, the EC2637 version seems to match this amp, or at least the modification. It is a 21-Jun-01 dated modification.
This mod puts a large 47 uF cap across the second stage cathode resistor, R10, but the design overall is different. The bright switch circuitry is moved to the 3rd stage cathode rather than the 2nd stage. It is possible that leaving out jumper W4 and the wire from W4 to R17 moves the bright switch to the 3rd stage.
The odd thing is that the service manual has a circuit board with the 2001 date that I think would match the EC2637 version, but ours is built on a circuit board that has 1996 printed on it. Perhaps they wanted to use up a supply of 1996 circuit boards.
That manual has several versions of the schematics, the EC2637 version seems to match this amp, or at least the modification. It is a 21-Jun-01 dated modification.
This mod puts a large 47 uF cap across the second stage cathode resistor, R10, but the design overall is different. The bright switch circuitry is moved to the 3rd stage cathode rather than the 2nd stage. It is possible that leaving out jumper W4 and the wire from W4 to R17 moves the bright switch to the 3rd stage.
The odd thing is that the service manual has a circuit board with the 2001 date that I think would match the EC2637 version, but ours is built on a circuit board that has 1996 printed on it. Perhaps they wanted to use up a supply of 1996 circuit boards.
Well, if all they changed were say component values, then the boards wouldn't need to be different. I suspect if they had a stack of leftover boards it would cost them more to engineer their newer circuit into the older board, than it would be to just knock out extra new boards. Fender's cost on a board is SOOOO much less than it costs you or I to stuff one. I think when they run out of boards is when they decide to redesign the boards so more than one model can use it.
If I were to hazard a guess, I'd think your 1996 board was late in the phase, and they made updates to the extent possible before the redesign took over.
I find the manuals interesting because they usually have a lot more information than the lone schematic pages floating around the internet. Sometimes the parts list answers questions.
If I were to hazard a guess, I'd think your 1996 board was late in the phase, and they made updates to the extent possible before the redesign took over.
I find the manuals interesting because they usually have a lot more information than the lone schematic pages floating around the internet. Sometimes the parts list answers questions.
Perhaps I wasn't clear, there is certainly a design change from 1996 to 2001, ours IS a 2001 built on a 1996 board. The 1996 has the bright switch on stage 2, that is disabled and a large cap is there now, 47 uF exactly as in the 2001 design. What I have not confirmed is if the wire moves the bright switch to stage 3, I think it does and then that makes at least these changes match the 2001 design. They would not have put the additional capacitor on stage 2 if it was just value changes.
I will trace it out with the schematic in hand to verify and report back here but I'm 99% sure that this was a factory ECO.
The ECO has W4 jumper removed, has R10 going from one hole for R10 to the lower hole for W4 and it has a 47 uF cap across it.
There is a wire from the upper hole for W4 going to the lower hole for R17.
I will trace it out with the schematic in hand to verify and report back here but I'm 99% sure that this was a factory ECO.
The ECO has W4 jumper removed, has R10 going from one hole for R10 to the lower hole for W4 and it has a 47 uF cap across it.
There is a wire from the upper hole for W4 going to the lower hole for R17.
Last edited:
It depends if you want to stick to the data sheet or not. The 6L6WGB is equivalent to the old 5881 which has 400v max plate, 300v screen and 26 watts per tube. The screen is exceeded by quite a bit, around 180 volts. Here's the data sheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/087/6/6L6WGB.pdf
Like Enzo says, not too much to worry about wattage-wise but I might think twice about the screen voltage and MAYBE the plate. I suppose you could use a larger screen resistor, thus dropping voltage and power at the same time. This is Tung Sol's sheet. Who knows about Sylvania's? Just something to consider.
http://www.mif.pg.gda.pl/homepages/frank/sheets/087/6/6L6WGB.pdf
Like Enzo says, not too much to worry about wattage-wise but I might think twice about the screen voltage and MAYBE the plate. I suppose you could use a larger screen resistor, thus dropping voltage and power at the same time. This is Tung Sol's sheet. Who knows about Sylvania's? Just something to consider.
Last edited:
There is a story about 7027 guts being stuffed into a variety, especially Sylvania, 6L6 types and many people say that the JAN WGBs have 7027 guts. The guts do not look at all like 5881 types but much more like 6L6GC/7027 so I might try them. GBs and GCs do look a lot alike but I've read that the plates are different but these being JAN types helps me to believe that they are better built.
I'll think about it a bit more and maybe do a bit more research.
Here is the claim about the guts:
www.thetubestore.com - Siemens 6L6WGB (made by JAN-Philips) Audio Tubes
That IS the smallest bottle that I've seen to claim to have the 35W guts.
I'll think about it a bit more and maybe do a bit more research.
Here is the claim about the guts:
www.thetubestore.com - Siemens 6L6WGB (made by JAN-Philips) Audio Tubes
That IS the smallest bottle that I've seen to claim to have the 35W guts.
Those are good no question, But you need them Tall Bottle top/side getter xD, or some STR387s etc some of the best. I wouldn't worry too much about that little amount of whatever Plate dissipation 30w is fine..how many are going to really wind em up anyways? Most don't, most are going to loaf around on more colder side. Screens have always been exceeded/run pretty hard, worried a lot more about that than, I ever will with plate's
Last edited: