Blackface Deluxe non-reverb servicing

Ronno25

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I dont think that is the original speaker, it should have an Oxford in it, ceramic not alnico.
My guess is it's worth $1500-1800 also, but could be worth more on a good day.
Yes, I think you're right. I got mixed up with the oxford speaker model numbers. The alnico one in this amp is labeled 12K5R-1 dating to either 1958 or 1968.
 

Ronno25

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I noticed that the coupling caps circled in red are .047 in my amp. Did the AA763's actually use .033 as the diagram suggests? Screen Shot 2022-09-05 at 11.40.29 PM.png

Edit* looks like I've answered my own question by finding an AA763 Deluxe with .033 coupling caps. Although most of the supposed AA763 amp pics I found had .047 caps.

Perhaps this suggests my amp was a "prototype" or experiment done in the transition from AA763 to AB763
 
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schmee

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I noticed that the coupling caps circled in red are .047 in my amp. Did the AA763's actually use .033 as the diagram suggests? View attachment 1025284

Edit* looks like I've answered my own question by finding an AA763 Deluxe with .033 coupling caps. Although most of the supposed AA763 amp pics I found had .047 caps.

Perhaps this suggests my amp was a "prototype" or experiment done in the transition from AA763 to AB763
Yeah, Fender seemed undecided on that cap value in other amps too IIRC. It seems to change from the AA version to the AB version switching those two values.
 

Wally

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The midrange caps were interesting in the BF/SF era. We see that they settled on the .047mfd for the AB763 and later DRs. The other amps used the .047mfd cap there from the beginning except for the Super Reverb, Concert, Pro, and Vibroverb amps. The Pro and Vibroverbs followed the DR with the AA763 using that .033mfd and chang8ng to the .047mfd in the AB763. The Super Reverb and Concert amps used a .022mfd. The Super Reverb changed to the .047 in 1977 with the ULtraLinear circuits.
maybe that midrange cap difference is one thing that people like about the SR???? I have been known to revoice Fender amps to acquire a second channel that is not a mirror image of the other channel.
 

Wally

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Yes interesting, I used to play the normal channel on my DR quite often. I play the non reverb Deluxe a lot now, I think it's pretty similar, but just from memory, not able to AB them, as I sold the DR a couple years ago .

The Normal channel in fender reverb amp is the same as the Notmal channel in a non-reverb amp….two gain stages. The Normal channel in the AA864 and AA165 Bassman amps are the same topography, too. The AB165 Bassman Normal channel has three gain stages….and that is why it is the hottest BF guitar channel…bar none…because there is no reverb and trem circuit to suck gain. That trem circuit 8n the non-reverb amps Vibrato channel is why that channel is weaker than the Normal channel, too.
 

schmee

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The midrange caps were interesting in the BF/SF era. We see that they settled on the .047mfd for the AB763 and later DRs. The other amps used the .047mfd cap there from the beginning except for the Super Reverb, Concert, Pro, and Vibroverb amps. The Pro and Vibroverbs followed the DR with the AA763 using that .033mfd and chang8ng to the .047mfd in the AB763. The Super Reverb and Concert amps used a .022mfd. The Super Reverb changed to the .047 in 1977 with the ULtraLinear circuits.
maybe that midrange cap difference is one thing that people like about the SR???? I have been known to revoice Fender amps to acquire a second channel that is not a mirror image of the other channel.
My guess was that the Super was pretty huge on the low mids and low end with the 4 x 10 so they went to the .022 uf.
 

Wally

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My guess was that the Super was pretty huge on the low mids and low end with the 4 x 10 so they went to the .022 uf.
If they were concerned about low end, then why did they not reduce the bass cap???
 

Lowerleftcoast

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Do you have a higher resolution version?
Hah, no.
All I did was a cut and paste with the addition of a few lines.
Below is a version with the .047 caps in the tone stack.

I can visualize the circuit better when looking at a schematic so I threw it together. No sense in not sharing when it seems to be a variant or possibly a prototype of what Fender did long ago.

Deluxe-schematic-chassis-A00658-.047.jpg
 
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schmee

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If they were concerned about low end, then why did they not reduce the bass cap???
I'm not sure really, but it seems to work. Not sure what freq's are effected by those caps and where they crossover, what interaction each pot has with others etc....?
 

Wally

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I'm not sure really, but it seems to work. Not sure what freq's are effected by those caps and where they crossover, what interaction each pot has with others etc....?
the only way to know would be to install a .047mfd cap in a Super Reverb and hear the difference. I have never reduced the mid cap value without also reducing the Bass cap value. I have never increased any of the values for those caps.
 

Lowerleftcoast

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If they were concerned about low end, then why did they not reduce the bass cap???
Fender usually reduced the bass by minimizing the coupling cap just before the PI. This schematic shows .001uF. The high pass filter with this coupling cap has a cutoff frequency of about 155Hz. The low E string fundamental is ~82Hz, so in this case, the low E fundamental is about 9dB less than the D,G,B, and high E string fundamentals. That is significant, imo. It seems, in those days, Fender liked to keep all of the harmonics generated in the preamp, then they would reduce the bass content to lessen woofiness.
 

Wally

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Fender usually reduced the bass by minimizing the coupling cap just before the PI. This schematic shows .001uF. The high pass filter with this coupling cap has a cutoff frequency of about 155Hz. The low E string fundamental is ~82Hz, so in this case, the low E fundamental is about 9dB less than the D,G,B, and high E string fundamentals. That is significant, imo. It seems, in those days, Fender liked to keep all of the harmonics generated in the preamp, then they would reduce the bass content to lessen woofiness.

and….circa 1980-1971, Fender increased that coupling cap to a .01mfd. Some people prefer this. It warms an amp up. Some people even go larger than .01mfd.
ime, careful control of the tone stack in the preamp with regard to the volume setting is the solution to the problem of the signal going to piec3s in the preamp…..whether those are high or low frequencies.
 

David Barnett

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Fender usually reduced the bass by minimizing the coupling cap just before the PI. This schematic shows .001uF. The high pass filter with this coupling cap has a cutoff frequency of about 155Hz. The low E string fundamental is ~82Hz, so in this case, the low E fundamental is about 9dB less than the D,G,B, and high E string fundamentals. That is significant, imo. It seems, in those days, Fender liked to keep all of the harmonics generated in the preamp, then they would reduce the bass content to lessen woofiness.

What is the impedance that 0.001uF cap is looking into?
 

Lowerleftcoast

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What is the impedance that 0.001uF cap is looking into?
The most direct route I see is through the 1M grid leak then the tail and shunt resistors. I am sure you are asking due to the other 1M, the 0.1uF cap, and the Global Negative feedback resistances. Of course you may be asking due to the *other* signals as well.

I may be totally wrong but imo/ime the direct route will make for a close enough estimate of the impedance for the RC filter feeding the PI. I just discount the other impedance. The 1M and .1uF cap in parallel with the tail resistor makes little difference to the total. Likewise, the NFB loop will make little difference to the total.
 

Ten Over

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The most direct route I see is through the 1M grid leak then the tail and shunt resistors. I am sure you are asking due to the other 1M, the 0.1uF cap, and the Global Negative feedback resistances. Of course you may be asking due to the *other* signals as well.

I may be totally wrong but imo/ime the direct route will make for a close enough estimate of the impedance for the RC filter feeding the PI. I just discount the other impedance. The 1M and .1uF cap in parallel with the tail resistor makes little difference to the total. Likewise, the NFB loop will make little difference to the total.
The effective input impedance can be in the order of twice the nominal grid leak resistance without NFB and four times the nominal resistance with NFB. In this example, the grid leak is 1M and the effective input impedance is 1.8M without NFB.
LTP Figure 3B Schem PNG.png
LTP Figure 3B Dialog PNG.png
 

Paul G.

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My guess was that the Super was pretty huge on the low mids and low end with the 4 x 10 so they went to the .022 uf.
Yes, Fender varied those mid caps, in addition to the PI coupling caps depending on the speaker configuration.
The 45 watt Master Volume amps all share the same schematic, with an asterisk footnote for the Pro Reverb (.047uf, fixed 6.8k mid) as opposed to .022uf with mid pot for the others.
 

schmee

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Fender usually reduced the bass by minimizing the coupling cap just before the PI. This schematic shows .001uF. The high pass filter with this coupling cap has a cutoff frequency of about 155Hz. The low E string fundamental is ~82Hz, so in this case, the low E fundamental is about 9dB less than the D,G,B, and high E string fundamentals. That is significant, imo. It seems, in those days, Fender liked to keep all of the harmonics generated in the preamp, then they would reduce the bass content to lessen woofiness.

and….circa 1980-1971, Fender increased that coupling cap to a .01mfd. Some people prefer this. It warms an amp up. Some people even go larger than .01mfd.
ime, careful control of the tone stack in the preamp with regard to the volume setting is the solution to the problem of the signal going to piec3s in the preamp…..whether those are high or low frequencies.

What is the impedance that 0.001uF cap is looking into?
Yes that PI coupling cap makes a big difference. I learned of this and was quite surprised a couple years ago. There was a thread here on TDPRI about it. I had a Bandmaster Reverb that just was too bright on the top end no matter what I did. The kind of spikey brightness that is on the very top end. After reading a bunch of old notes I had from a Jeff Gehring post regarding OT problems with BMR's, I experimented and changing that cap made a huge difference. It's quite different than just changing the tone cap values, as the PI cap seems to make a more global change. If that makes sense.

Old notes to myself: (not 100% correct I imagine):lol:
"Phase Inverter Coupling Cap : Blackface head amps used a 500pF coupling cap and the combo amps used a .001uF like the BMR amp. Fender used the smaller cap to trim some bass because the matching blackface extension cabs were closed back and had extended bass response. If you play mostly clean or use mostly open back cabs the .001uF cap would probably be best, but if you play a lot of overdrive the 500pF might be best for a tighter overdrive tone.

I did that with a single 15 and it sounded real good. The only thing I changed in the circuit was the phase inverter input cap. I went with a .005 replacing the original 500pf. >(= .0005uf)
Other values:
SF Vibrolux = .01 uf

BF VV = .001 uf

BF Pro Rev = .001 uf

.005 uf = 5000 pf

---- UPDATE: I TRIED THE .01 PI COUPLING CAP in the BMR AND IT WORKS GREAT."
 




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