The 1977 Princeton Reverb Repair Part 1

Part 1

A couple weeks back a local customer emailed me regarding a Lil King S he had acquired on the used market in the Asheville area. It was an easy fix, but it had a changed cab and a few other things done to it. NO matter, I got that thing fixed right up for his next session! I will cover that one in a future post. He mentioned that he had a 1977 Princeton Reverb that had been acting up and when I met him to pick up his S he brought the PR with, so I could have a look. I was hoping from the description, it would be an easy tube swap or solder joint touch up, “Sounds great for an hour then drops volume and or reverb fades”, you know, boilerplate, my old amp isn’t working right stuff.

I don’t normally do repairs, but if it is a vintage Fender, especially a Princeton Reverb (PR), I will do the work…mainly because I have all the parts on hand to build a new one, so a repair is usually pretty straight forward. Also, I love to hear the old ones as they are usually all a bit different. Some of this is obviously based on the work that has been done to them over the decades, and also, the production process back then was not the most consistent, supplies could change, multiple people building the amps, etc.

I was also thinking I could test this amp out against Lil King (LK) #700 that I had just finished up for Deke Dickerson. Once I got it in the shop, I turned it on to burn it in and see if I could replicate the issues. Sometimes these intermittent issues can be the hardest things to track down. I’d rather have an amp that won’t turn on or has a smoked resistor…Intermittent usually means you’ll hear something along the lines of “it’s working fine here on my bench” back from your amp guy…Then maybe a bench fee, and you take it home, with a emotional cocktail of hope and skepticism…To turn that damn thing on, and then almost immediately, it does the thing again!!!

Back to the tech, repeat and so on…it is NO fun for anyone involved. I know what both sides feel like…in my other posts I have referenced this, take it to a tech and not know what it will sound like when it comes back…Even when it is just some new tubes…it’s agonizing as a player…and as a consumer!

I, of course didn’t hear any of the volume drop or cutting in and out. Jacks seemed fine, tubes seemed fine…I had not even opened the amp up yet, just plugged in and listened. I always try to approach it as a player first…Play the thing and LISTEN. Well I a/b’d it briefly with #700, using a long speaker cable from my bench, I plugged the LK into the PR cab with the (seemingly) original 10” speaker as well as into the bench LK Cab that has a well broken in Alessandro GA-SC64 speaker. First thing I noticed…man the PR was really bright and edgy on the top end and upper-mids…through both speakers. The reverb was also way off…cranked to 6 it wasn’t as present as the LK on 3…There was definitely something off. The LK was way warmer and more responsive…I am confident in the job I do replicating these old Fender’s and that the 70s ones are generally considered “close” to “ok but a little bright” but this was a ways off…This was not a fair way to compare…and Deke was ready for his amp. I decided the a/b test at least in terms of playing would need to wait so I could inspect the 77 and ship Lil King #700 out west.

Opening up the chassis really filled me in on what was going on

There was obvious work done inside, some good, some not so good, the reverb issue was because someone omitted the bypass cap on the reverb driver tube (v2 12AT7)…this was why it didn’t have the lush wash out of a normal Fender reverb. Also, there were quite a few metal film resistors (very stable voltage wise) in key spots, and honestly, in completely random spots as well

The Plate resistors on the pre-amp tubes are the ones you may have heard or heard about, the term, popping, cracking, sizzling or a combination of any of those when they go bad…seeing these replaced is pretty common. I have my beliefs on this, and there are MANY more, most, by guys that probably know more than me about electronics and very likely, everything else…But I do know that in the pre-amp plates, that is where this carbon composition resistors shine for tone, you want the voltages to drift…that is what the old amps did…SO that was the first order.

I assume they didn’t have some of the common values for Fender amps…btw, if a tech tells you he doesn’t stock say a 100k 1/2 watt resistor, he probably doesn’t work on many Fender amps. You may need to seek a second opinion for the repair. To remedy not having the a few 100k’s, and a couple 56K’s he just wired two resistors together to attain the value needed. I replaced all of that with the 1/2 Carbon Composition type to get it as close as I could back to stock

Stay tuned for part 2 and maybe 3 if it is needed…Next we get to the power tubes, rectifier tube and check out the differences between the 64-67 and this 1977 Princeton Reverb

NEXT WEEK:

“The missing bypass cap may have been intentional. The work was not subpar, it may have been a “fix” for the washed out reverb that happens on Fender amps above 4, generally speaking. I had never thought of that one, so there again, someone knew what they were doing, electronically speaking…. “

What are the differences between the Lil King and Lil King S?

…and what’s this I hear about a Lil King X?

First let’s start with the Lil King…first built in 2004, at that time, there were NO Princeton Reverb Chassis available in the boutique amp supply chain, and I know this because the few big companies that were around back then did not have one yet…I am sure someone, some where probably had a few made or bent and welded one themselves, but for someone looking to produce a replica on the fledgling boutique amp market like myself, there was nothing out there. I had an old silver face PR and had a company blueprint the metal work and produce them for me. Several LONG months later it was done and by late 2004 I had the FIRST Lil King built and ready to send to David Wilson (RIP) of The Tonequest Report for review. Back then I had to build and sell these things so I could pay for the parts to build more. (I have a story about how I got the very first Lil King back…YES, I sold the first one to buy the parts for more!!) One of the great things about replicating after years of playing these old Fenders was that prototyping was not nearly as important as when you build something that is tweaked or completely NEW in design. That, as you know, is not something I do, I build replicas, “flaws” and all! I did not borrow ANY money to start Headstrong, it was literally amp to amp back then.

The Lil King is a faithful reproduction of the AA1164 Black Panel Princeton Reverb, and at that time, trust me there was NO ONE building these for the commercial market. I did not tweak anything in the circuit to change the bass response or clean it up etc. Just built this thing as close as I could to an old one. Side note, I did side by side tests of a few GOOD vintage examples that I had access to, as you know there can be a huge variance in these old amps…Some sound good or great while others are just off for a variety of reasons.

The Lil King Reverb is built around one of the GOOD vintage examples and after nearly 20 years and 700 ( I am building chassis no. 700 this week for Deke Dickerson) of the stock Lil King amps of which I have personally wired EVERY ONE, I am confident that its as close as it gets…Not saying it is better than anyone else’s take, just as close as it gets!

The idea for the Lil King-S (the S stands for “Souped up” or “Stage” ) came in 2009 after several years of building the Lil King and people asking me about beefing the amp up or tightening the bottom end. There are a few popular Princeton Reverb Mods out there as you know, but I wanted to take it further…This is one of the few times in the 20 years I have been building amps that I even considered doing this. To me one of the main reasons Princeton Reverb’s sound the way they do is the Phase Inverter (read the Blog, “why do the Princeton Reverb and Deluxe Reverb amps sound so different” for more on this) I wanted to keep that, otherwise I am building a single channel Deluxe Reverb basically. I wanted all that sag to happen like a Princeton, but much louder and cleaner on the way to that point. I boosted the PI voltages by using the untapped leg of the Filter cap can, bumped some voltages in other places, but mainly…I had a HUGE Princeton Sized Power transformer built AND a 35 watt Output transformer built with a special primary impedance so that it would handle a variety of power tubes. It was my thought that is I beefed up all of this, but kept the PI the same, the amp would land at about 25 watts with 6L6 tubes. SO the main difference in the stock Lil King (black panel Princeton reverb AA1164) and the Lil King S is the transformer set and higher voltages across the board…The effect of this has also been explained in previous Blog posts, so please check those out if you are so inclined!

Lil King S (left) and stock Lil King (right) power transformers built to my spec by Heyboer

The Lil King-X…Well that is what I call a “flex” model between the two amps. There is a significant amount of room between the Lil King and at the Lil King-S, so over the years I have talked to so many people about what they wanted out of the amp I was building for them, that the X took shape. Charlie Hunter was one of the first to have one built. He had several Lil King and Lil King S amps, but sometimes there was too big of a gap between them for certain rooms. The X can be many things…The one I just built for JD Simo, is Lil King S power transformer, Deluxe reverb output transformer, it will run 6V6 or 6L6s, for 18-22 watts. PI voltages were raised, but pre amp voltages were kept close to the stock AA1164 readings. I have done so many different versions of this to achieve what someone wants…stock LK power transformer with a Deluxe reverb output to juice it just a little, Lil King S power transformer with stock Princeton Output and 6V6s…a ton of voltage mods to clean or brighten…It is virtually endless.

I personally prefer the stock versions of both, but there have been some cool variations. Rest assured, this is not nearly as complex or vast as it seems, these are finite incremental changes, some of which are so subtle, only guys like JD and Charlie Hunter can really tell the difference…subtle changes to mids, volume, headroom, and compression…these are guys that are TRUE MASTERS of what they do and have done it for so long, they can hear these little 1-5% changes….Not to discourage anyone from exploring this, but lets not over think this thing…Call me and I can walk you through some of this…it is not something that you should obsess over, I can get you where you need to be based on the information you provide.

Lil King-S (left) and Lil King (right) Output transformers built to my specs by Heyboer

Between the Lil King, the Lil King-X and the Lil King-S, I have built almost 1000 chassis, so I have heard most if not all of it at this point…There is a reason guys call me about this circuit…And I am not one to brag, but I do think I have earned the right to consider myself a bit of an authority on the Princeton Reverb and what makes them sound so good!

I hope you enjoyed this latest 5 AM rant! Time to get to work on Lil King No.700!!

Thanks for reading!!

As always, you can call or email me ANY time with questions and feel free to comment below!

Wayne

Why do the Princeton Reverb and Deluxe Reverb amps sound so different?

Did you ever think to yourself, “why do the Princeton Reverb and Deluxe Reverb seem to sound so different?” They are technically both “Blackface Fender” amps, they both have reverb in the circuit…but why is the Deluxe always a bit brighter, cleaner and louder?

The obvious differences between the Princeton and Deluxe reverb amps are wattage, transformers, cabinet size, 10” speaker vs 12” speaker, 1 channel vs 2 channels etc…This article is a bit more granular and nuanced than that.

I will try to keep this on guitar player level tech talk, that is, I will use terms that guitar players use rather than a bunch of terms that amp techs and electronic guys tend to use. I feel that is a strength that I developed early on in my 20 year building career. Not alienating guitar players with a bunch of technical talk…Sometimes guys with a more electronic based background, who lack knowledge of the tone terms (as well as dealing with an eccentric group of people) we like to use a players, can get a little defensive and throw a bunch of big words at you…I prefer to use the vernacular that the players use and bridge the gap between the two sides of the fence so to speak.

I started as a player who knew NOTHING about why tube amps sounded so good other than, every time I played one, I knew that was the tone! Communicating with amp techs (if you could find one) could be dicey and uncomfortable at best. Leaving us wrought with anxiety over how our amp was going to sound when they finished the “work”. Not wanting to offend anyone, was NOT my forte in those days…and I remember a few times the “old guy in the back” gave me that look! How could “I” be wrong I thought, that guy is Full of it I thought to myself!..Yeah man, it was all him!

Fortunately times have changed and there are of course many great options now, but in the 90’s, no internet, no forums etc, you were shooting in the dark with techs.

Now, back to the topic at hand

To me the Princeton reverb still has a foot in the Tweed and Brown era tone. I feel this is due in large part to the Phase inverter section of the amp. In the old days, Fender used what is referred to as a “split load Phase Inverter” meaning that the phase inversion is accomplished by using only half of the 12AX7. The 12AX7 is known as a dual triode…two sides, 3 pins on each side (plate, grid, cathode). Make sense? By only using half of the tube to do the job, like using 3 of the 6 cylinders in your car, it is inherently less efficient than the Long Tail pair type found in other blackface amps, such as the Deluxe reverb and all other BF amps above it. The Tweed Deluxe, had the split load as well. Basically this means the signal is less powerful heading to the power tubes so the sag and break up happens much earlier. Also, to my ear, it is a bit darker and lacks a little of the scooped mid sound of the rest of the Blackface Fender amps above it. The other difference in the Princeton Reverb from other Blackface amps is in the tremolo…The PR has the Bias Vary/Wiggle circuit. This uses the power tubes to modulate the bias to create what I think is one of the most swampy, bluesy tremolo sounds they ever did. This type of tremolo is also found in the Brown Vibroverb, Princeton and Deluxe. (NOTE: It is not to be confused with the only true “Vibrato” Fender did in the Brown Concert, Super, Pro and Bandmaster…That is a completely different beast and I will go over that in a future article. FYI, I will be building that Brown Super this year!) In closing, the Princeton Reverb, to me is still a Brown Princeton, but with the Blackface reverb circuit added. Fender kept the Princeton Reverb virtually the same until the early 70’s barring a few adjustments and general butchering.

The Deluxe Reverb is VERY different from a Brown Deluxe, thus different from a Princeton reverb as well. This is where I feel the real blackface tone people are referencing comes from. Cleaner, brighter, scooped mids etc. The tremolo circuit is also different, Fender moved to the Opto-coupler based tremolo that basically modulates the volume to create the tremolo effect, and to my ears is a little less organic sounding. Still a cool sound, and obviously, used by many legends over the years. They stuck with that circuit on all the other Blackface amps from that era as well. The other difference is the “Long Tail Pair” phase Inverter (both sides of a 12AT7 powered this) making it more efficient, brighter, slightly higher voltages across the amp. The first stage filter caps were also higher than a Princeton so it is a bit tighter. The voltages on the power tubes are significantly higher in Deluxe Reverb amps as well. Some are as high as 470V (JD Simo’s DR is that high at 120v!!!) You often see, “will handle the high plate voltages of a Deluxe Reverb” in some 6V6 power tube descriptions. This is what they mean!

For reference, The Royal Reverb, the Headstrong Deluxe Reverb replica comes in at about 425-435 VDC (Volts DC) @120 volts (AC from the wall). By contrast the Princeton Reverb came in at 400-415 VDC…The Lil King is usually 400-410 VDC range.

Pre-amp gain stage (V1 and V2) voltages are a bit higher in the Deluxe Reverb amps. 170-180 VDC on the plates of the 12AX7 tubes (vs. the Princeton reverb pre-amp plates at 150-160vdc). I think this may be an under discussed topic…The higher the plate voltage on those pre-amp tubes, the cleaner and brighter the sound. The lower voltages, like in a Tweed amp, you get a darker tone…less spike in the notes. Finding a balance between the two is what I try and do when someone wants to tweak the amp a little to their liking. Rather than make these big changes to the circuit, sometimes a small resistor change will get you what you need without drastically changing the tonal character of the amp that you loved. Thus avoiding a case of diminishing returns.

So in closing, the main differences electronically between these two amps is why you may have noticed a big difference in these two amps. Some people may feel, the Princeton Reverb is just a lower watt Deluxe Reverb and that is just not the case. The Princeton will always be darker, softer on the bottom end, less spiky on the top end as well as much easier to carry around to the gig!

I could keep rambling on this topic for days, but I also have to actually build these things! As always, thanks for reading and thank you ALL for the 20 years of support! I still can’t believe this is what I get to do all day!!

Talk soon,

Wayne

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