Deluxe reverb clone Output transformer question

[pdf64]

I may bypass the choke and use a resistor instead. Maybe that will get the B+ up and be less draw on the PT

I don't see how that would make much of a difference in normal use; maybe if it was being continuously heavily overdriven then the output tubes may conduct a little more with the choke, thereby loading the power supply more. But I wouldn't bother persuing that change.
The rectifier just needs a couple of high voltage diodes (>=1200V PIV) and monster resistor.

[imaradiostar]

Jamie - Thanks. I am running JJ 6v6's. They sound pretty good and are reliable. Since I have a 9 pin EZ81 in it I can't just stick SS 8 pin Rectifier. I will just make one and see. I am thinking I may bypass the choke and use a resistor instead. Maybe that will get the B+ up and be less draw on the PT.

Thoughts anyone??

No need for an 8 pin solid state rectifier. Simply solder two 1n4007 diodes across the tube socket (internally) with the banded ends toward the cathode and the non-banded end toward the plates.

Generally the choke in a small Fender amp has a much lower DC resistance than a dropping resistor such as the one used on a Princeton reverb. End result is you'll see more voltage (and cleaner DC) with a choke in most cases. I'd stick with the choke.

5K isn't exceptionally low for a pair of 6v6's but it's lower than I'd usually use. I had a pair of JJ's running at into 11k load the other night and they seemed to be doing just fine, even at about 500 volts. The screens were run on lower voltages, of course.

What is your idle cathode current and how are you measuring it? If you're using the 1 ohm resistors as shown in the linked schematic I'd look for 15 to 20 millivolts (.015 to .020) across each of them. As low as your voltages are I'm wondering if it's running the 6v6's really hot. At idle there shouldn't be much voltage drop across that EZ81. I've found they're pretty robust and can take more than the data sheets would lead you to believe.

Maybe I'm crazy but I'm of the opinion (and regularly argue with my studio engineer cousin) that Fender reverb amps are hi-fi with their boosted treble and scooped mids and are useless for anything resembling distorted settings. My tastes in music and amplifier construction seem to reflect this. I know there are distorted Fender tones out there but I think they're at their best clean like Eric Johnson's tone, not dirty like SRV's.

If you WANT a Fender to sound more distorted and midrangy then it's an easy mod- change the first stage cathode bypass cap to say... .68uf and lift the bottom of the mid control to bypass the tone circuit. It'll get way dirtier and thicker. If it's too harsh clip the treble cap on the reverb blend circuit. The tone controls will be useless then but it'll sound cool.

PS- i thought I had posted this last night but I somehow forgot to- I bet it's because I have a 1 month old son and sleep is only coming in little bits here and there!

jamie

[pdf64]

Simply solder two 1n4007 diodes across the tube socket

I think that the 1000V PIV rating for 1N4007 would get pushed in this application - I think they 'see' twice the peak voltage, then factor in line regulation and the transformer regulation voltage in standby.
BY127 or BY448 would do it.

[imaradiostar]

I think that the 1000V PIV rating for 1N4007 would get pushed in this application - I think they 'see' twice the peak voltage, then factor in line regulation and the transformer regulation voltage in standby.
BY127 or BY448 would do it.

Nah, I think you're overthinking it. If it's a 330 volt transformer (660 vct) each plate lead has a peak +- voltage of sqrt(2)*330=466 volts peak. A 1n4006 would take this in stride, though a 1n4007 makes more sense. I have several amps in operation with 440 volt (880 vct) secondaries and single 1n4007's as rectifiers with no trouble.

If you're worried about it use a pair of 1n4007's in series on each side. Put .1uf caps across each to make sure the load is balanced.

jamie

[JoeM]

4007s are cheap, I'd use 2 (at least) in series.

[GregS]

I haven't looked at your schematic as I don't click links when I'm at work but I'm suspecting your master volume. Depending on how you install it it is possible to create a high pass filter with the coupling cap at the grid of the PI. Your tone can change with the sweep of the knob as the resistance to ground varies in this network.

Anyway, before concluding your output transformer is a problem see if your tone changes at various settings of your MV and if you can solve this tone problem simply by having your MV in a different position. If this is the case and you've installed your MV how I'm thinking there is a simple fix that involves adding some resistance between the wiper of the MV and the coupling cap at the PI. This ensures there is at least a certain amount of resistance to ground from the cap and won't attenuate your signal level much either.

Greg

[Wrongdog]

Do you think post PI MV would be better?? I just built it per the old Steve Luckey schematic (that is now gone).

The post PI dual ganged ones I do in my 18 watters and my Bedrock Royale Reverb clone I built work pretty well.

I will mess with it soon. I will mess with present MV and change to the SS rectifier. BTW - I don't like a lot of gain, at least for this amp. I want that "big" but moderate volume BFDR tone. I don't have the $$ for a real one!


Cminor9 it is not THAT hobbled. Its my build slop and changing things when I don't reaslly know what I am doing....

I posted a few pics. I hope they work since I never did it before

Thanks for everyone's input so far.

[GregS]

Do you think post PI MV would be better?? I just built it per the old Steve Luckey schematic (that is now gone).

I've never tried one before so can't comment on that.

I suggest simply trying out your amp and seeing if the tone changes with different MV settings. If not then your MV is not likely the cause of your tone issue.

[pdf64]

If it's a 330 volt transformer (660 vct) each plate lead has a peak +- voltage of sqrt(2)*330=466 volts peak.

jamie, I pretty sure that's incorrect. The cathode of both diodes will charge to the peak positive value, +446.6V in this case. However the negative trough of the ac cycle from each transformer leg will be peaking at -446.6V. Therefore the total peak voltage across each diode will be 933V.
Factor in a high line supply and unloaded transformer condition, say 5% for each, and 1000V is exceeded.

I have several amps in operation with 440 volt (880 vct) secondaries and single 1n4007's as rectifiers with no trouble

From the above calculation, my take on this is that you've been lucky. The manufacturers must be building them tough, perhaps able to meet a higher spec than they are guarenteeing. They have the option to do that, in fact they coud make 2000V 1A diodes and package them as anything from 1N4001 to 1N4007 - they would meet the spec; however, if any failed above 1000V, they would be justified in rejecting liability.
If it's your own stuff then fair play to continuing good fortune, but it would be risky to incorporate this into a customer's equipment / commercial design.
Pete.

[imaradiostar]

oh, you're totally right. Each end of the secondary swings to +/- 1.414 times above and below ground, making 2.828*vac. I guess I have been lucky!!

Thanks for pointing that out. I believe I've had FWCT and FWB arrangements confused. That could get expensive in time!

jamie

[Wrongdog]

Maybe this thread holds an answer - The California Dreamer schem is flawed according to this:

http://music-electronics-forum.com/t25964/

[imaradiostar]

That's got to be a contribution. I went back the schematic you posted and it would appear to me that the 2x220k resistor network after V3B is built backwards. It would be easy enough to replace the 220k to ground with a 50k after the series 220k and before the .001 uf PI cap. You could even install a trimpot to determine if less PI distortion is part of the tone you like.

jamie

[Wrongdog]

Ok - I haven't got a clue why but I think we are on the trail to success! I just got done noodling with the amp and it really is almost there.

Thanks all - Knoob with a soldering iron and internet connection.......

[J M Fahey]

Shenglu, just post your Led Flashlight SPAM, donīt bother to write technical sounding meaningless answers.

[Wrongdog]

Okay - re-did a few things and it is MUCH better.

I fixed a few freaky flaws in the California Dreamer schematic that I used. The 12ax7 reverb/ tube had BOTH cathodes to one 820 resistor and one 22/50v bypass cap??! I separated them to two 1.5k/.22uf and that opened up things a lot and stopped the squeal of the reverb that occurred when turned past half (never use it that wet. I was using a 5751 tube there and now I can use a 12ax7 which of course gave me way more bass. I did a suggested split load resistor thing before the V3b and B+ that I found on another thread. I also put a 56k resistor to ground after the .1 cap and 220k resistor after the V3b before the PI.

I did not change the rectifier yet.

Thanks to all for helping me. I really am just learning all this stuff. Its amazing that my home brews work at all...