66 deluxe reverb - can the original PT run a 5u4?

[Jasonpatrick]

I compared the non-reverb amp with the reverb amp normal channel again.... and they actually sound very similar. It seems you're spot on here. I think I'll just accept the reverb channel for what it is and let it be a bit bright, icepicky. Turns out they invented this thing called a tone knob on the guitar.

Lower your bias and see if it’s still ice. 65 70 is too high for a fender. Try 50 and see if it gets warmer. That 60-70 rule is not always the rule. I have fenders that are running at 45% .. anything above 60 and they stop sounding like fenders and they start sound like azz.
Also, try a variac. Drop the line voltage down like when they ran gz34s… or just stick a 5u4gb in it and call it a day.

 

[Ronno25]

@Jasonpatrick I tried every possible bias from cold to hot, sounded best to me where it is now.

 

[King Fan]

Ice pick? Are you running the original speaker? I'd be slow to try to fix icepick with voltage changes; tons of iconic DRs must be running those vintage high voltages. Have you played other old DRs? DRs with different speakers? But a variac or bucking transformer is a fun, safe way to find out if 'browning' the sound suits your taste.

Now. Here's a different way (what, me?) of thinking about the schematic change, going from GZ34 to 5U4 between BF and SF. Wally's right, of course, they didn't show the voltages changing -- so that suggests the PT did change.

Except, we're talking about Fender schematics -- where voltages are often inconsistent. We recently discussed the VibroChamp, where the later schematic jumped B+ up a ton but didn't change B+2 and so on down *at all*. What if Fender just neglected to update the voltages on the DR schematic? And the PT with the same number *is* the same PT, as @Jasonpatrick insists?

*Then* you'd be fine to run a 5U4 with a 1966 PT.

Ain't it funny how we know so little about these old (and fundamental) Schumacher and Triad PTs?

 

[marshman]

Unless you've got a one of those fancy laser thermometer guns and at least a few 5U4GBs sitting around for trial purposes, I'd be starting elsewhere than the rectifier trying to tame some icepick.

I'd start by tracking down at least one 5751 and a 12AT7 for the reverb side, put the 5751 in (looks like )V2, first tube in the verb/trem channel, and then put the 12AT7 in the PI (V6) slot. Nothing guaranteed, lots of those tubes vary in tone across brands and even tube to tube from same factory, but if you have a tube brand you like, that would probably be the cheapest place to start. Shoot, you could probably learn something just by switching V1 and V2 around.

Speakers are a little more expensive and a bit more work to change, but can also have a huge impact on your tone.

I did have a very tangentially related question, though: Will reducing the load on the 6V heater winding east the load on the 5V winding, too?

 

[Lowerleftcoast]

Ice pick can be addressed early in the circuit like the Bassman AB165. The Bassman has a .01uF cap in parallel with the plate resistor in the Bass channel. IIRC, Marshall did this as well. Alternatively, Marshall used a cap from plate to cathode on V1 to perform the same function.

Ice pick can be addressed before the PI. Hot Rod Deluxe/Deville have a cap across the MV (essentially a 390p - 1000pF from signal to ground). The Blues Jr does something similar before the PI.

Ice pick can be addressed later. Simply putting a cap parallel to the NFB resistor is a typical mod.
Marshall increases the 47pF snubber cap found on the 5F6A Bassman to 220pF which phase cancels highs in the audio frequencies as well as ultra high frequencies. The JCM 900 has a 100pF parallel to a PI plate resistor to scrub off some highs.
The Vox cut control uses that phase cancelling cap/pot setup to reduce highs.

It is your choice where in the circuit to reduce highs. Be aware there are harmonics that develop along the signal path, so where they are reduced makes a difference. You may like them reduced early or late in the circuit.

Choosing the cap size for the amount of high reduction proves to be very much to taste. Try several different values to suit your ears.

 

[Jasonpatrick]

Ice pick? Are you running the original speaker? I'd be slow to try to fix icepick with voltage changes; tons of iconic DRs must be running those vintage high voltages. Have you played other old DRs? DRs with different speakers? But a variac or bucking transformer is a fun, safe way to find out if 'browning' the sound suits your taste.

Now. Here's a different way (what, me?) of thinking about the schematic change, going from GZ34 to 5U4 between BF and SF. Wally's right, of course, they didn't show the voltages changing -- so that suggests the PT did change.

Except, we're talking about Fender schematics -- where voltages are often inconsistent. We recently discussed the VibroChamp, where the later schematic jumped B+ up a ton but didn't change B+2 and so on down *at all*. What if Fender just neglected to update the voltages on the DR schematic? And the PT with the same number *is* the same PT, as @Jasonpatrick insists?

*Then* you'd be fine to run a 5U4 with a 1966 PT.

Ain't it funny how we know so little about these old (and fundamental) Schumacher and Triad PTs?

Speaking of schematic voltages , isn’t the power transformer in the 65 Princeton, PR and champ all the same? Yet all three show different voltages.. then you have the Princeton schematic with a 5u4gb and one with a gz34 and they have the same voltages on the schematic.. same power transformer… I had a friend digging in to a 59 super and none of the voltages where even randomly close to what the schematic said even at 110-117 volts, every part was in perfect working order and what the schematic called for as well.

 

[Wally]

Gotcha. But following that logic, I hope they send ya the right one with the same part number for the amp you need it for… see, doesn’t make sense. If I take my 1969 deluxe reverb with a gz34 in it with 120v at the wall it’s gonna be high , like 450-60. If I take the same amp through my variac at 117 its spot on 415 ish…Now, if I take the same amp at 120v from the wall with a 5u4 in it, guess what happens.. from a manufacturing stand point, if wall voltages are creeping up, what’s the easiest most cost effective way to change the amp? Redesign a transformer that we have tons of in the warehouse or change a rectifier tube?

Regarding the last sentence there, I have to observe that when we start watching date codes on these old Fenders we find that sometimes the transformers were dated at the Schumacher factory fairly closely to chassis date codes that were done during and after construction of the amp. The same is true of speakers.…sometimes a matter of weeks, sometimes a matter of a few months. I would guess that Fender did not have a huge warehouse full of a two year supply of transformers.
I might think that the change to the 5U4 was made with forethought for one of two reasons…or maybe for both reasons. The cost of good, true GZ34s might have weighed in the decisions. My ‘63 has an OEM Mullard GZ34.…a true GZ34. The American 5U4 was a known Quantity with a proven record. Maybe the growing production of English amps using the European GZ34s drive the price of those rectifiers up by the middle of the 1960s??? The change would have been thought out ahead of time. .fender certainly did not go to the 5U4 to change the voltage in the amp…because the schematics from both ‘eras’ remained the same at least for the DR. So, if the voltage did not drop with the 5U4, one wonders why that is?? There is only one answer…the specs changed while the model number stayed the same.…at least that is how I see it. YMMV…
and….it matters to me not at all what tube someone puts in an amp unless the amp is mine or is one I have worked on. If a person insists on running a 5U4 in a BFDR on which I have worked, I will explain my misgivings about doing so as well as the precautions to take if they do so. It would also be understood that doing soup has a thing would negate any responsibility I might have for the welfare of the amp.
Y'all have a good one…..

 

[Ronno25]

Ice pick can be addressed..

This is an awesome summary of options. I did the vox cut pot in a princeton reverb clone I built and it is fantastic. I love that mod. It took away all the stuff I don't like and left all the stuff I do like. I suppose I could put that where the ground switch is.

Edit: one thing I particularly like about this mod is that it is dynamic. The phase cancelation changes depending on the volume of the amp. At lower volumes you get less (and imo need less) and when the amp is cranked up the cut control knocks down some of the harsh high end.

 

[Ronno25]

I've been considering trying the eminence ga-sc64 12" to see if that does what I want with the high end. But I am concerned it'll be similar to the eminence cannabis rex, which to my ears sounds big, stiff and dull. I do not like highly efficient, big-magnet stiff speakers. I like inefficient speakers so you can crank the amp up without your ears bleeding. what type of volume am I looking at with the ga-sc64 12"?

 

[Chipss36]

Many blackface clones , reissues, or even a real one, with a new and not yet broke in speaker , of a fresh recone, can be an ice pick, how much playing time has happened with the current speaker? And at what volume levels? Over how long?

some speakers need a considerable amount of break in before they settle in, stiff spiders, new doping, the fibers in the cone, all need to move a bunch before they all kinda gel together.

I cringe when I blow a evm, they take a very Long time to get broke in after a recone. They go from ice pick city, to smash face punchy and sweetness once broke it. Especially the 15”s.

I would play the heck out of it, and loud, and know it takes longer than most think, if that’s a new speaker, before changing anything with the circuit. Or yet another speaker swap.

even the current stock reissue blackface speakers are the same way, ice pick when new, but get much better once truly broken in.
It’s something to consider.

 

[Ronno25]

@Chipss36 I've tried it through 4 speakers that are familiar to me and that I like in various amps. It came to me with an EV force 12 that I'm planning to replace. But not sure what to get for it yet.

 

[Dacious]

I've been considering trying the eminence ga-sc64 12" to see if that does what I want with the high end. But I am concerned it'll be similar to the eminence cannabis rex, which to my ears sounds big, stiff and dull. I do not like highly efficient, big-magnet stiff speakers. I like inefficient speakers so you can crank the amp up without your ears bleeding. what type of volume am I looking at with the ga-sc64 12"?

The SC64 is 40 watts so it's not a high wattage unit. It is very efficient at 99db SPL. You might be better with something like a Jensen mod or VOR vintage-type speaker which are 95-96db.

 

[SoK66]

The best option with vintage amps vs modern wall voltages is some kind of a buck transformer, Brown Box, Tone Preserver, home made, etc. They will bring down the wall voltage to the 115 -> 117vac the amp was designed for, you can then retain the 5AR4/GZ34 recifier and all is good.

 

[Ronno25]

Alrighty, I put an early 60's oxford 12j4 ceramic magnet speaker in it and it now sounds fantastic. Problem is i'm doubting the power handling of this speaker. Anyone know if these speakers have a chance of managing a deluxe reverb? They seem equivalent to the Jensen C12r

 

[Wally]

I've been considering trying the eminence ga-sc64 12" to see if that does what I want with the high end. But I am concerned it'll be similar to the eminence cannabis rex, which to my ears sounds big, stiff and dull. I do not like highly efficient, big-magnet stiff speakers. I like inefficient speakers so you can crank the amp up without your ears bleeding. what type of volume am I looking at with the ga-sc64 12"?”

Find you an Oxford 12” from 1966 or later….12K5-6, 12L6, or 12T6.
Those low efficiency Oxfords will cut the volume level in half com8ng from a 100db speaker.
And….the Alessandro 64 sounds nothing like that hemp cone Cannabis .Rex. The only hemp cone speaker I have heard that I liked is the Emi 820H in a champ. In that amp, the darkness of the hemp makes for a bigget low end in an amp that usually doesn’t have much down low.