Brown Deluxe/Constellation build...help please...

[ChrisM]

You said you used a 25/25 cap but in the pics I see a 25/50. Good thing, 25V would have been pushing it.

[dehughes]

Yeah, it's 25/50...sorry. The heaters are DC...my "supply" is on the left of the pic...on the side of the chassis.

The tubes are actually dissipating over 16w...which explains in part why it sounds so good! HA! I'll try running a 5Y3 and see if that helps...which I'm sure it will... Too funny...

[dehughes]

So, with a JAN Phillips 5Y3 in there, I'm getting 362v on the plates, 22v across the cathodes, giving me 36.7ma per tube and about 12.44w per tube. Better. Not exactly 80%, of 14w, but better than 16.7something.

[dehughes]

So, here's the thing: I REALLY like the tone of the amp when it's running super hot (5AR4), but I know there's no way I can seriously expect the 6V6s to last when they're dissipating 16.7w each. What's more, the tone of the amp is much "harsher" when I'm running a 5Y3, and I'm beginning to think that it's not a function of the power tubes. I think it's more preamp voltages instead, as I tried different power tubes and rectifiers, and I find it hard to think that the power section is going to sound "harsh" when it's dissipating 88% of it's maximum.

SO, I'm inclined to think that what I'm hearing might be in part a function of the preamp voltages rising and lowering, with the lower voltages causing the harshness. What I've found is the following:

---------------------5AR4------------------5Y3

*All readings are volts DC*

OT CT--------------419--------------------363
6V6 plates---------413--------------------359
6V6 cathodes-------26---------------------22
After 1k resistor---405-------------------351
After 10k resistor--338-------------------293
PI plates------------251-------------------218
12AX7 1st plate----171-------------------149
12AX7 2nd plate --189-------------------165
6SN7 1st plate-----133-------------------116
6SN7 2nd plate----136--------------------118

So, I guess my question is, what value of resistor should replace the 10k resistor in order to, with a 5Y3 rectifier, keep the power tubes running where they are yet bring the voltages in the preamp up to where they would be if I was running a 5AR4. I think that's where I need to go with this... Does that make sense?

[tubeswell]

So, I guess my question is, what value of resistor should replace the 10k resistor in order to, with a 5Y3 rectifier, keep the power tubes running where they are yet bring the voltages in the preamp up to where they would be if I was running a 5AR4. I think that's where I need to go with this... Does that make sense?

You want to lower the supply resistor. Try different ones to see where you get to. You might need to halve the value (i.e. 4k7) to get any noticeable increase in plate supply voltage and/or sonic difference.

[dehughes]

Yeah, I know I need to lower the resistor...I was just wondering if 1) anyone had the techy smarts (I sure don't...) to figure out what value would yield the voltages I'm looking for, or 2) if my thoughts were correct in assuming that what I'm experiencing could indeed be a result of bumping voltages down or up in the preamp as opposed to the power section.

I may have a 4k7...I'll take a look, and at worst tack in another 10k in parallel to see what comes of it.

[dehughes]

I just tacked in another 10k in parallel with the existing 10k dropping resistor, and that brought the voltages not quite in between the two extremes, but more on the high side of the middle ground. That's just about perfect, in terms of being able to tell if low-voltage is really the cause of the harshness I'm hearing in the upper midrange. The "high" side of the two extremes was a bit much anyway....kinda smacking those preamp tubes around.

I'll play test it tomorrow and see if this solved my harsh-at-low-volume problem. If it does, I have a few 4k7 that I'll measure for value and find one that gets me where I want to go. If not, I'll be tinkering some more...

Thanks!

[dehughes]

So, interesting discovery...

The harshness is gone now that I lowered the B+ dropping resistor. Good deal!

However, I noticed that with this new PT I'm forced to run a 5Y3 in order to keep the voltages where they need to be in the power section. With a 5Y3 and the lower B+ resistor the voltages are exactly where they need to be, but what I've noticed is that when the amp is cranked, I'm not getting the same breath and sustain out of it as I was before, with a lower voltage PT, a 5AR4, and the higher dropping resistor.

What I've inadvertently done is keep all things (plate voltages, etc.) relatively equal and then hear the difference between a 5Y3 and a 5AR4 in the same amp. What I've discovered is that a 5Y3 seems to kinda choke off a cranked amp...less air, sustain, more squishy and compressed. Usually when I've swapped 5AR4s for 5Y3s I've never adjusted resistors, etc., to compensate for the drop in B+, so I've never heard what JUST the rectifier does to the power section. Now that I've heard it, I'm inclined to say that I prefer a 5AR4 when it comes to the "cranked amp" vibe.

Am I missing something here?

[Firestorm]

Try a 5V4GT tube. The 5Y3 is directly heated (and hence somewhat lossy). The 5AR4 and the 5V4 are indirectly heated so the geometry can be smaller. They are "airier" sounding (in fact, I like NOS 5V4s almost as much as Mullard GZ34s.)

You may have to tweak your dropping resistor again. Voltages will be somewhere between the GZ34 and the 5Y3.

Another thought -- you can run a separate (larger) dropping resistor to supply the screens (and the associated cap). The preamps can run off the the regular higher-voltage B+ string.

In a tetrode or pentode, the screen IS the anode (in terms of setting the operating point). The plates just catch the elcctrons and transfer the signal, so keeping SCREEN voltages lower tames the tube.

[tubeswell]

Well a 5AR4 will make your tubes and OT work a wee bit harder and make your speaker(s) sing a bit more. A 5Y3 would definitely be mushier, but then a 5Y3 is an older type of tube made for an earlier era of (lower powered) amps.

[dehughes]

Good ideas...I'll try a 5V4 and maybe a 5U4 as well.

I think what's going to happen is that I'm going to have to go BACK to a lower voltage PT as well as a 5AR4, as dropping voltage via the 5Y3 just ain't the same as having a 5AR4 and lower voltages from the PT.

Wish I'd known that beforehand...but lesson learned!