princeton preamp

jim milewski · From: stowe, vermont

any ideas how to use a fender princeton as a preamp into a vegas? my options are grabbing the signal after the last preamp tube and maybe using a stepdown xformer to make the signal low enough as to not overdrive the vegas or using a dummy load instead of the speaker and tap it there, any ideas, as the princeton develops a nice tone, now if I can get it out there

ajm · From: Los Angeles

You seem a little familiar with electronics by the lingo you used.

Why not use the extension speaker jack (I think it has one) and get a couple of resistors and/or a pot. You could put a voltage divider with the resistors on the jack inside of the amp. This way you would get the sound of the power tubes through the slave amp and you would also still have the Princeton working as a monitor.

If it seems a little brittle sounding, try putting a capacitor across the output.

Gerald Weber of Kendrick has written several articles on how to do this.

ajm · From: Los Angeles

A couple of thoughts since my previous comments.

If you do it the previous way, then as long as you don't use the extension speaker jack for a speaker and only use the internal speaker the amp will play stock.

Also, many speaker attenuators have an output to tap off a lower level signal in addition to the one for the speaker. I don't know if these have this feature (you'll have to check) but I'm talking about the Scholz Power Soak, Kendrick/Trainwreck Airbrake and the THD Hotplates as an example.

jim milewski · From: stowe, vermont

I tried the extension with the main plugged in...no go the main speaker acts as a microphone, it seems I'll take the amp head out and look for the schematic, find several places to tap and measure voltages (signal)try resistors to cut voltage or a step down xformer...is the kendrik article on the web...thanks

Dan Tyack · From: Olympia, WA USA

Get a THD Hotplate, it will not only provide a line level out, it will also provide a dummy load for the amp (critical for preserving the health of the amp).

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www.tyacktunes.com

ajm · From: Los Angeles

Jim, there may be a misunderstanding here.

First, you need to leave the amp speaker plugged in. Also, for tube amps in general, don't ever run it without a speaker or equivalent load. The amp will go bye-bye, in particular the output transformer (not cheap).

With the speaker plugged in, use the extension speaker jack as the tap, but you'll need to step the voltage down. Using two resistors you can determine how much signal you feed to the slave amp. You need to consider not only the resistance values but also the wattage used. Also, if you just plug straight into the extension jack without stepping the voltage down, you could damage the input to your slave amp by feeding it way too much juice.

This is pretty easy to do but kind of hard to describe here. Try calling Kendrick in Pflugerville, Texas. My guess is the article is also reprinted in one of their books. It was originally in Vintage Guitar Magazine a few years ago. Also, any competent service tech should be able to do this for you.

Jay Ganz · From: Out Behind The Barn

If you want a clean signal, the speaker jack is not the way to go. You or your amp tech can just tack on
a coupling capacitor right where the input
goes to the 12AT7 tube (which feeds the 6V6's).
Then run a shielded wire to the extra speaker
jack (disconnect the original wires from it).
When you want to use the preamp ONLY just pull out the two
output tubes (6V6's) & you're set!
You can actually feed a signal out from any
stage in the preamp, the furthur back towards
the input jack, the cleaner it'll be.

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...and here's who taught me everything I know: CLICK HERE

Bill Rowlett · From: Russellville, AR, USA

Hi Jim,

I did this with my Blackface Bassman 50. I just tapped off after the last preamp mixer tube and went directly to a jack. I did install a DC blocking capacitor, but the voltage was low enough that I really didn't have to do that. It is just a safety net. I didn't need a transformer. I just pull the output tubes like Jay says.

Hope this helps,

Bill

[This message was edited by Bill Rowlett on 29 March 2000 at 08:58 AM.]

jim milewski · From: stowe, vermont

AJM thanks for the info, i do understand the damage that can hurt the output with no speaker load ( I plan to keep the speaker connected as a sort of monitor so a power soak won't work) and the damage to the input with a high current source (output from speaker jack)I tried a 50 watt dummy load on the speaker out and plugged a cord from ext. speaker to input of the vegas, with volume very very low, I get a bad hum, I think I will pursue a tap inside the front end circuitry ( I have a signal generator and Oscope) then I may capacitor couple or xformer couple to a padded down circuit ( my emmons has an average signal voltage aroun .75 to 1.25 volts, this is not peak to peak) my circuit post princeton and pre vegas should be about that I guess, like most things the problems will be keeping unwanted noise down and keeping a true undistorted signal. The tube sound is doing it for me, it realy sounds good, when I saw buddy e in new york in around 77 he had a emmons rosewood d 10 into a stock speaker twin with no effects (actually the big E is an effect no matter what he plays through!) anyway tone city, I still may fork out some rare cash for a super or a twin...I'll keep you posted and thanks for the interest and advice

jim milewski · From: stowe, vermont

jay , sounds good and your credentials and references are good, but that guy who showed you everything you know I would expect him to play a "wooden" neck guitar.
Come to think of it and I saw it right up close in 77, Buddy Cage ran into 2 showman heads with the output tubes yanked and fed the signal to a couple of crowns, again, do the math.... emmons into fender into 740 watts crown (they didn't bother even miking buddy) into 4 speaker cabinets ( 2 were deep and 2 were shallow partial open back cabinets with jbl d 130 and d 140 speakers) 2 speakers per cabinet, 8 total!) I also saw emmylou with hank devito using wooden neck emmons through a music man 130 watt tube amp

Dan Tyack · From: Olympia, WA USA

Taking a preamp output from the Princeton is fine, but the power amp adds as much if not more to the overall sound as the preamp.

Try the THD Hotplate, you will like it. You can either leave the speaker plugged in, or you can turn off some or all the volume to the speaker, and have the Hotplate soak up the power output, it's up to you.

On another note, you might try using a low output preamp as the first one in the preamp (Au7??). The tube guys know what I am talking about.

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www.tyacktunes.com

jim milewski · From: stowe, vermont

Dan I wondered about the effect the output tubes had on the sound, as you know many amps were made with solid state front end and tube output,what is the cost of the hotplate, maybe they can be made home rolled (I have some high wattage dummy resistors) I appreciate all this feedback

Bill Leff · From: Santa Cruz, CA, USA

For a completely different take, try running a Line6 POD using one of the Fender simulations ('65 Deluxe Reverb, '59 Bassman or '52 Deluxe) and make sure the speaker emulation is turned off. Run the line out of the POD into the effects return of the Vegas (I don't know these amps but assume it has one).

I've been using a POD fed to a Mesa Boogie Mark 1 power amp to a 12" EV and it's been a ton of fun. I don't play PSG but it works well with guitar and lapsteel. Sounds great with the band and has a pretty convincing tube feel.

jim milewski · From: stowe, vermont

is a pod a device, an effect, does musicians friend have them, are they much money? listen to this, I ran my steel thru a pandoras box and into the vegas post preamp input with a mid range cut speaker emulation it sounds pretty good! this little thing the size of a pack of king sized cigs is my total preamp and has large hall reverb

Bob Metzger · From: Waltham (Boston), MA, USA

Try this:
1) use a 12AY7 as your 1st preamp tube: It will give you more headroom with the hotter steel guitar output and probably sound better. If not , go back to the other tube!
2) have a preamp out installed on the Princeton by your favorite amp tech: use the extension speaker jack or the Vibrato (tremelo) jack on the back panel so you don't have to drill. I did this for a bass playing friend of mine a few years back and he loves it. I used a 'switched' jack (that's a jack that besides making a connection has one or more switches built in that can switch anything you'd like, related or unrelated) and when it was plugged in, it put the power tubes on 'standby' (removing the cathodes from ground, and eliminating the possibility of injuring your amp) and this amp head effectively became a preamp. Of course, you could, if you wanted, have a rear panel switch that allows you to determine if you want the power amp and in or not (sound or no sound out of the Princeton).
Use a good quality, large value coupling cap off of the plate of the 2nd preamp tube. You may have to tweak some preamp values to maximize the sound for steel guitar but any competent tech should know how to do that. Two other things: 1) putting a bright cap across the volume control sounds great for steel but keep it small like 47pf. 2) a middle control works wonders for steel also. I usually remove the two input jack assembly, save it for later restoration, put in a new input jack, use a 1meg and a 33k resistor (the tech will know) install THAT in the #1 input and put a 10K audio pot in the #2 input and wire it up like a Twin. Then you can control the mids much better than before. For the 'ultimate', use the 'power amp in' on your 2nd amp or have one installed at the same time you do this stuff. Good luck.

Bob

Dan Tyack · From: Olympia, WA USA

Jim the POD is cheap ($250 street) and sounds way, way better than the Pandora (which is good but not great). IMHO and YMMV, of course.

It would be possible to home brew something like the THD hotplate. I know nothing about the electronics involved, but I have tried a bunch of dummy loads (home brewed and comercial), and the THD just sounds a lot better. Or put another way, it changes the sound a lot less. They aren't cheap, but aren't bad. And they won't kill your amp!

Disclaimer: Andy Marshall at THD is a friend of mine and I do help him beta test equipment, although he doesn't pay me in any way (free stuff or $$) to say anything about his products.

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www.tyacktunes.com

jim milewski · From: stowe, vermont

Bob thanks for the great info so if I get a twin shematic just duplicate the middle circuit and use the jack hole for a pot. is this tube sub you gave me a higher gain than a 12ax7? I saw the POD in musicians friend if it does what it says it must be great

Jay Ganz · From: Out Behind The Barn

Here's a list of preamp tubes in order of most to least gain:

12AX7

12AT7

12AY7

12AU7

Bob Metzger · From: Waltham (Boston), MA, USA

Jim,
The 12AY7 has less gain than the stock tube, the 12AX7, but will offer more 'headroom' before distortion and very well may have a sweeter tone. It allows you to tinker with the gain structure of the amp without going inside and soldering alot. The gain the amp has now is designed for an electric guitar signal, whose pickups have a weaker signal than most steel guitar pickups, generally speaking. But, if you have both tubes, play the amp with one tube in it for awhile, then switch to the other tube and play that one for awhile. Pick the one that sounds best to your ears. For me, 'awhile' could be as long as 2 weeks. This tube's location is the first tube on the right, if you are facing the rear of the amp.

Yes, Jim, just get a Twin Reverb schematic and/or layout and follow the wiring but here's the whole explanation:
This amp has no midrange control but instead has a 'fixed' amount of mids via a 6.8K resistor wired, usually, to the bass pot (if you install the middle pot, you will remove this resistor). Instead of having one fixed amount of mids, the 10K pot gives you a variable amount of mids that might be advantageous when you play in different surroundings and acoustical environments. All Blackface and Silverface Fender amps with a 'middle' control are wired the same way in relation to this middle control, as is the Twin Reverb. Look at any old Fender schematic with a middle control and you'll be ok. If you don't feel comfortable doing this, hire a tech to do it. Remember, amps have lethal voltages stored inside, even when turned off and unplugged from the wall.

Generally speaking, these are simple mods that will make a big difference in the sound of the amp.

Good luck,

Bob

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