6L6s in a Princeton Reverb?

Brewbaker · October 15th, 2004, 12:05 PM

I've upgraded to a Deluxe OT and was now thinking about trying 6L6s for a different sound. Looking for a small jazz amp and figured I should try to make my SFPR work for that before buying something else. My plan is to use a 12AY7 in P1 for low gain, clean. Then the 6L6s for a little more umph and low end punch. I already have a 12" baffle with a Weber 12F150A which sounds pretty good, but I may try swapping a California Ceramic 12 if it will fit. What I'm wondering is will I have to go to a larger power transformer to use the 6L6s?

fullerplast · October 15th, 2004, 12:33 PM

You would need a larger PT for 6L6's.

Two more things you can do are the Stokes mod and the Paul C mod. These raise the voltage to the phase inverter and balance it better. Along with what you've done so far, that's about as far as I would go with the PR. Anything more and you may as well just get a DR or VR.

Tim Swartz · October 15th, 2004, 12:35 PM

The Princeton Reverb's power transformer will meltdown due to excessive filament winding draw. It uses the same PT as a Champ, so it is already taxed w/ 2 6V6s and a bunch more preamp tubes than a Champ.

TDPRI · October 15th, 2004, 02:39 PM

Not all that much difference. I experimented with 6L6's in my PR. It was the stock transformer, but with a Celestion Vintage 30 speaker.

I didn't want to hurt anything so it was an "at home" test with only a couple of hours of use. But I didn't see a great difference in sound. More bottom end and a bit more headroom... maybe. But not a dramatic huge difference in my amp.

Paul Green

Tremo · October 15th, 2004, 07:38 PM

I strongly recommend against using 6L6s in a Princeton. And I now no longer recommend the phase inverter mods either. It can overstress and damage the PT. Read the thread on this over on the Amp Workshop board. It's in the tubes forum, thread re the JJ 6V6.

jhundt · October 16th, 2004, 04:47 AM

has any of us ever actually had a transformer melt down or blow up when using 6L6's in a 6V6 amp? I know that many advise strongly against it, and I understand the reasoning. I also know that many of us use the 6L6's anyway. But I want to see if the predicted damage has actually occurred to anyone, and if so, what was the extent of the damage to other components? If I need to replace the transformer anyway, can I just play the old one 'til it goes out?

My home-built Vox-type amp probably breaks just about every rule for max voltage on the tubes and current on the transformers. I always expected it to blow, but it turned out to be totally reliable, and sounds really good.

TREMO - thanks for directing us to that board, I wasn't familiar with that one. I'm not able to locate the thread you mentioned, but I'll keep looking.

jhundt · October 16th, 2004, 06:28 AM

I was looking at an old version of the Amp Workshop, now I found the current one with the thread Tremo mentioned. Thanks again for the link.

fullerplast · October 16th, 2004, 11:17 AM

Quote:

Originally Posted by Tremo

I strongly recommend against using 6L6s in a Princeton. And I now no longer recommend the phase inverter mods either. It can overstress and damage the PT. Read the thread on this over on the Amp Workshop board. It's in the tubes forum, thread re the JJ 6V6.

Thanks for the info, good analysis and very interesting discovery! I bet nobody was more surprised than you...

Now who's gonna send out the recall notices???

Tremo · October 16th, 2004, 06:13 PM

I think Ron Veil (Uncle Spot) has had two Princeton PTs melt down on him. I have damaged two myself. Enough. Sadly my PR will gather dust now until I can afford an Allen replacement PT.

The Amp Workshop thread is in the Tubes forum, the thread is the one regarding the JJ 6V6 field data.

And do NOT use 6L6s in a Princeton!!!!

trag-o-caster · October 16th, 2004, 10:03 PM

Quote:

Originally Posted by jhundt

has any of us ever actually had a transformer melt down or blow up when using 6L6's in a 6V6 amp? I know that many advise strongly against it, and I understand the reasoning. I also know that many of us use the 6L6's anyway. But I want to see if the predicted damage has actually occurred to anyone, and if so, what was the extent of the damage to other components? If I need to replace the transformer anyway, can I just play the old one 'til it goes out?

Right here! Blew my Champ by doing just that. I can't exactly remember the extent of all the damage, but it was a fairly costly fix for a lowly Champ. I'd advise against trying until the transformer goes out. I'm not that knowledgable, but it seems like it could be a fire hazard to me.

Tim Swartz · October 17th, 2004, 02:37 PM

I've probably serviced 6 or so Champs/VCs and Princetons/PRs with blown PTs over the years.

Tremo · October 17th, 2004, 07:47 PM

Guys, bear in mind that the PT in a Princeton/PR is a CHAMP unit, so it's stressed to the max right from the get-go. Now if you start modding (no Torres!!!), and start increasing the load on the PT, you're on very thin ice, so don't be surprised if something takes a crap on you. You have been warned.

eugenedunn · July 9th, 2008, 03:36 PM

'Glad I found this thread regarding 6L6-type substitutions for 6V6GT's.

I see from a tube reference chart that 6V6GT's use 6.3 heater volts and 0.45 heater filament amps to run.

I also see that 6L6 type tubes use 6.3 heater volts, but 0.9 heater filament amps (twice the 6V6 requirement).

A Princeton using a 5AR4 rectifier tube is also supplying 1.9 amps to that tube.

Let's say you use a Weber Copper Cap (WZ34), which uses NO FILAMENT current. That means you're saving 1.9 amps current draw, but still supplying in-rush-limited rectified power.

Could you then safely use a pair of 6L6-type power tubes in a SF Princeton safely? I reasoned because you're saving 1.9 amps current draw by using the Copper Cap, the amp should be able to tolerate the 0.9 amp increase in power tube filament requirement for the 6L6 power tubes. You're actually 1.0 amp below normal usage.

I thought about trying this to not necessarily get more volume (I know the OT is the limiting factor here), but maybe beef up my bass response and clean headroom. My amp has been recapped and serviced recently.

Anybody have considerations I may have missed? Thanks for any insights you can give. I know some people like the change, others go back to the 6V6.... I am interested in all these types of subs, trying to understand how it affects tone for different applications.

Anyway, this seems safe to me on paper..... thoughts?

Bob Arbogast · July 9th, 2008, 04:43 PM

Quote:

Originally Posted by eugenedunn

A Princeton using a 5AR4 rectifier tube is also supplying 1.9 amps to that tube. . . . Let's say you use a Weber Copper Cap (WZ34), which uses NO FILAMENT current. That means you're saving 1.9 amps current draw . . . Anybody have considerations I may have missed?

What you've missed, apparently, is that the rectifier has its own, 5V filament winding. Relieving that winding of a 1.9A draw will reduce the overall heat load on the PT, but the 6.3V winding itself may still be substantially over-stressed by a 6L6 pair.

Bob Arbogast

eugenedunn · July 9th, 2008, 04:58 PM

Thanks Bob....... for pointing out that separate winding issue. I can see how that current load might not be diminished with the power tubes.

Can anybody else corroborate whether that separate 6.3 volt winding will withstand the 6L6's? Or where would I find specs of that power tranny to verify that the 2 6L6's will be safe in this specific application?

RedRock · July 9th, 2008, 05:55 PM

I have installed a 6.3V 3amp small auxiliary transformer in a Princeton
Reverb to heat the 2 6l6 tubes. The filament line was separated
right after the power tubes, and the amp transformer was connected to
the preamp tube heater wires. The auxiliary transformer was connected
to the on-off switch, and its center tap connected to chassis ground.
It worked fine. The amp transformer even ran a little cooler because
its heater load was reduced by 1.2 amps.
In my opinion, the 6l6s provided more top and bottom, and greatly
improved the tone. Of course you have to re-bias after you
install them. The auxiliary transformer was about $10 from Mouser,
and was mounted next to the power transformer.

eugenedunn · July 9th, 2008, 06:08 PM

RedRock..... that was a cool answer about the tone aspect.

I found the reference that the original 125P1 power transformer is rated 6.3 volts at 2.0 amps for that section. So it appears that if I use two 6L6-type tubes (running 0.9 amps each), I'll only be riding about 1.8 amps. That's 10% below spec.

Seems to be worth a try and there's a relative margin available, providing I use the Weber Copper Cap.

RedRock · July 9th, 2008, 06:14 PM

I should also mention that the stock Princeton Reverb
transformer runs way too hot heating the 6l6s by itself.
If you don't want to go the auxiliary heater transformer route,
Dave Allen at Allen Amplification sells an upgraded drop-in replacement
power transformer, the TP25, with 150 ma., 5V at 2A for the
rectifier, and 6.3V at 4.5A for the heater line.
Since the 4 pre-amp tubes take 1.2A to heat, this leaves
3.3A for heating the power tubes. This will easily take care
of the 1.8A the 6l6s need, and even allow the use of EL34s.

sjhusting · July 9th, 2008, 06:24 PM

Quote:

Originally Posted by eugenedunn

RedRock..... that was a cool answer about the tone aspect.

I found the reference that the original 125P1 power transformer is rated 6.3 volts at 2.0 amps for that section. So it appears that if I use two 6L6-type tubes (running 0.9 amps each), I'll only be riding about 1.8 amps. That's 10% below spec.

Well, then there are all those preamp tubes at 300 mA heater current each.

You either need a filament transformer or a beefier PT.

steven

RedRock · July 9th, 2008, 06:28 PM

Remember, the 4 preamp tubes need .3A each to heat.
That is a total of 1.2A right there. The 2 6V6 tubes in a stock
Princeton Reverb take .45A each, so that is .9A. Add the
preamp tube draw to the power tube draw, and you get a 2.1A
draw to heat all of the tubes in a STOCK Princeton Reverb.
Two 6l6s draw 1.8A, and when added to the preamp draw of
1.2A the total draw is 3A. This is well above the stock Princeton
Reverb power transformer heater winding spec, and should be avoided, in
my opinion. One needs an auxiliary heater transformer, or
an upgraded power transformer such as the Allen TP25.

eugenedunn · July 9th, 2008, 06:36 PM

Thanks again all for the insights. I love the depth of experience here. I see the implications of this substitution. It gives me appreciation of the original design spec.

Geno

Tremo · July 11th, 2008, 05:12 AM

My Princeton lives again, and now it has one of those heavy duty Allen replacement PTs. I've gigged the amp a couple times, cranked and it survives now. No more PT problems!

To run 6L6s, you need the Allen PT plus a 6L6 OT, the stock Princeton OT will gain you NOTHING with 6L6s, it's way too small.

RedRock · July 11th, 2008, 08:32 AM

Allen sells various 6l6 output transformers along with the
power transformers.

October 15th, 2004, 12:05 PM	#1 (permalink)
Brewbaker Tele-Meister Join Date: Mar 2003 Location: Cape Elizabeth, Maine Posts: 258	6L6s in a Princeton Reverb? I've upgraded to a Deluxe OT and was now thinking about trying 6L6s for a different sound. Looking for a small jazz amp and figured I should try to make my SFPR work for that before buying something else. My plan is to use a 12AY7 in P1 for low gain, clean. Then the 6L6s for a little more umph and low end punch. I already have a 12" baffle with a Weber 12F150A which sounds pretty good, but I may try swapping a California Ceramic 12 if it will fit. What I'm wondering is will I have to go to a larger power transformer to use the 6L6s? __________________ http://www.sonicbids.com/davidbrewbaker

October 15th, 2004, 12:35 PM	#3 (permalink)
Tim Swartz Tele-Afflicted Join Date: Mar 2003 Location: Michigan - Tweenst the Great Lakes Posts: 1,904	DON'T DO IT ! The Princeton Reverb's power transformer will meltdown due to excessive filament winding draw. It uses the same PT as a Champ, so it is already taxed w/ 2 6V6s and a bunch more preamp tubes than a Champ. __________________

October 16th, 2004, 04:47 AM	#6 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	who has experienced melt-down? has any of us ever actually had a transformer melt down or blow up when using 6L6's in a 6V6 amp? I know that many advise strongly against it, and I understand the reasoning. I also know that many of us use the 6L6's anyway. But I want to see if the predicted damage has actually occurred to anyone, and if so, what was the extent of the damage to other components? If I need to replace the transformer anyway, can I just play the old one 'til it goes out? My home-built Vox-type amp probably breaks just about every rule for max voltage on the tubes and current on the transformers. I always expected it to blow, but it turned out to be totally reliable, and sounds really good. TREMO - thanks for directing us to that board, I wasn't familiar with that one. I'm not able to locate the thread you mentioned, but I'll keep looking.

October 16th, 2004, 06:28 AM	#7 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	found the Amp Workshop I was looking at an old version of the Amp Workshop, now I found the current one with the thread Tremo mentioned. Thanks again for the link.

October 17th, 2004, 02:37 PM	#11 (permalink)
Tim Swartz Tele-Afflicted Join Date: Mar 2003 Location: Michigan - Tweenst the Great Lakes Posts: 1,904	I've probably serviced 6 or so Champs/VCs and Princetons/PRs with blown PTs over the years. __________________

October 15th, 2004, 12:33 PM	#2 (permalink)
fullerplast Tele-Afflicted Join Date: Mar 2003 Posts: 1,066	You would need a larger PT for 6L6's. Two more things you can do are the Stokes mod and the Paul C mod. These raise the voltage to the phase inverter and balance it better. Along with what you've done so far, that's about as far as I would go with the PR. Anything more and you may as well just get a DR or VR.

October 15th, 2004, 02:39 PM	#4 (permalink)
TDPRI Administrator Poster Extraordinaire Join Date: Mar 2003 Location: TDPRILAND Posts: 5,725 36 Photos	Not all that much difference. I experimented with 6L6's in my PR. It was the stock transformer, but with a Celestion Vintage 30 speaker. I didn't want to hurt anything so it was an "at home" test with only a couple of hours of use. But I didn't see a great difference in sound. More bottom end and a bit more headroom... maybe. But not a dramatic huge difference in my amp. Paul Green

October 15th, 2004, 07:38 PM	#5 (permalink)
Tremo Banned Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,803	I strongly recommend against using 6L6s in a Princeton. And I now no longer recommend the phase inverter mods either. It can overstress and damage the PT. Read the thread on this over on the Amp Workshop board. It's in the tubes forum, thread re the JJ 6V6.

October 16th, 2004, 06:13 PM	#9 (permalink)
Tremo Banned Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,803	I think Ron Veil (Uncle Spot) has had two Princeton PTs melt down on him. I have damaged two myself. Enough. Sadly my PR will gather dust now until I can afford an Allen replacement PT. The Amp Workshop thread is in the Tubes forum, the thread is the one regarding the JJ 6V6 field data. And do NOT use 6L6s in a Princeton!!!!

October 17th, 2004, 07:47 PM	#12 (permalink)
Tremo Banned Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,803	Guys, bear in mind that the PT in a Princeton/PR is a CHAMP unit, so it's stressed to the max right from the get-go. Now if you start modding (no Torres!!!), and start increasing the load on the PT, you're on very thin ice, so don't be surprised if something takes a crap on you. You have been warned.

July 9th, 2008, 03:36 PM	#13 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 839 37 Photos	'Glad I found this thread regarding 6L6-type substitutions for 6V6GT's. I see from a tube reference chart that 6V6GT's use 6.3 heater volts and 0.45 heater filament amps to run. I also see that 6L6 type tubes use 6.3 heater volts, but 0.9 heater filament amps (twice the 6V6 requirement). A Princeton using a 5AR4 rectifier tube is also supplying 1.9 amps to that tube. Let's say you use a Weber Copper Cap (WZ34), which uses NO FILAMENT current. That means you're saving 1.9 amps current draw, but still supplying in-rush-limited rectified power. Could you then safely use a pair of 6L6-type power tubes in a SF Princeton safely? I reasoned because you're saving 1.9 amps current draw by using the Copper Cap, the amp should be able to tolerate the 0.9 amp increase in power tube filament requirement for the 6L6 power tubes. You're actually 1.0 amp below normal usage. I thought about trying this to not necessarily get more volume (I know the OT is the limiting factor here), but maybe beef up my bass response and clean headroom. My amp has been recapped and serviced recently. Anybody have considerations I may have missed? Thanks for any insights you can give. I know some people like the change, others go back to the 6V6.... I am interested in all these types of subs, trying to understand how it affects tone for different applications. Anyway, this seems safe to me on paper..... thoughts?

July 9th, 2008, 04:58 PM	#15 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 839 37 Photos	Thanks Bob....... for pointing out that separate winding issue. I can see how that current load might not be diminished with the power tubes. Can anybody else corroborate whether that separate 6.3 volt winding will withstand the 6L6's? Or where would I find specs of that power tranny to verify that the 2 6L6's will be safe in this specific application?

July 9th, 2008, 05:55 PM	#16 (permalink)
RedRock TDPRI Member Join Date: Jun 2008 Location: Nevada Posts: 54	I have installed a 6.3V 3amp small auxiliary transformer in a Princeton Reverb to heat the 2 6l6 tubes. The filament line was separated right after the power tubes, and the amp transformer was connected to the preamp tube heater wires. The auxiliary transformer was connected to the on-off switch, and its center tap connected to chassis ground. It worked fine. The amp transformer even ran a little cooler because its heater load was reduced by 1.2 amps. In my opinion, the 6l6s provided more top and bottom, and greatly improved the tone. Of course you have to re-bias after you install them. The auxiliary transformer was about $10 from Mouser, and was mounted next to the power transformer.

July 9th, 2008, 06:08 PM	#17 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 839 37 Photos	RedRock..... that was a cool answer about the tone aspect. I found the reference that the original 125P1 power transformer is rated 6.3 volts at 2.0 amps for that section. So it appears that if I use two 6L6-type tubes (running 0.9 amps each), I'll only be riding about 1.8 amps. That's 10% below spec. Seems to be worth a try and there's a relative margin available, providing I use the Weber Copper Cap.

July 9th, 2008, 06:14 PM	#18 (permalink)
RedRock TDPRI Member Join Date: Jun 2008 Location: Nevada Posts: 54	I should also mention that the stock Princeton Reverb transformer runs way too hot heating the 6l6s by itself. If you don't want to go the auxiliary heater transformer route, Dave Allen at Allen Amplification sells an upgraded drop-in replacement power transformer, the TP25, with 150 ma., 5V at 2A for the rectifier, and 6.3V at 4.5A for the heater line. Since the 4 pre-amp tubes take 1.2A to heat, this leaves 3.3A for heating the power tubes. This will easily take care of the 1.8A the 6l6s need, and even allow the use of EL34s.

July 9th, 2008, 06:28 PM	#20 (permalink)
RedRock TDPRI Member Join Date: Jun 2008 Location: Nevada Posts: 54	Remember, the 4 preamp tubes need .3A each to heat. That is a total of 1.2A right there. The 2 6V6 tubes in a stock Princeton Reverb take .45A each, so that is .9A. Add the preamp tube draw to the power tube draw, and you get a 2.1A draw to heat all of the tubes in a STOCK Princeton Reverb. Two 6l6s draw 1.8A, and when added to the preamp draw of 1.2A the total draw is 3A. This is well above the stock Princeton Reverb power transformer heater winding spec, and should be avoided, in my opinion. One needs an auxiliary heater transformer, or an upgraded power transformer such as the Allen TP25.

July 9th, 2008, 06:36 PM	#21 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 839 37 Photos	Thanks again all for the insights. I love the depth of experience here. I see the implications of this substitution. It gives me appreciation of the original design spec. Geno

July 11th, 2008, 05:12 AM	#22 (permalink)
Tremo Banned Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,803	My Princeton lives again, and now it has one of those heavy duty Allen replacement PTs. I've gigged the amp a couple times, cranked and it survives now. No more PT problems! To run 6L6s, you need the Allen PT plus a 6L6 OT, the stock Princeton OT will gain you NOTHING with 6L6s, it's way too small.

July 11th, 2008, 08:32 AM	#23 (permalink)
RedRock TDPRI Member Join Date: Jun 2008 Location: Nevada Posts: 54	Allen sells various 6l6 output transformers along with the power transformers.