Vintage Kent DR45 Tube Guitar Amp AmplifierFiends, I can't say that I've EVER ran across an amp that has me scratching my head more than this Kent DR45. Most of us above the age of about 40 or so at least recognize the KENT name, as quite a few Kent branded electric guitars were sold during the 1960's and early 1970's. However, the amps are quite a bit more rare, and this model is nearly rare enough to be termed a "Ghost Amp". She's a cool ghost, too! With a pair of 12ax7 tubes in the pre-amp section and a pair of EL84/6BQ5's for the power section, complete with tube rectification and tube bias-oscillation tremolo ... well ... it's got all the right stuff! I came across this amp while negotiating a deal on a Silvertone archtop; the seller got a gleam in his eye and led me to a back room and said he had something he knew I'd love. He was right. It was this amp and a matching Kent Polaris II guitar, he made me an offer I couldn't refuse and away I went. I was told in advance that the amp did not work, and several days later I opened her up to see what ailed her. I was pleasantly surprised to find a very clean pseudo turret-board layout that looked very repair-man friendly. The filter caps all checked dead as a dornail, and so I replaced them with slightly over-value Sprague Atoms, checked all the other components and fired her up ... NOTHING! Hummm, other than a bunch of carbon resistors that had drifted out of spec, everything was perfect. Hummm. And so I did what we all do in these situations, I googled the amp for a schematic, that's when I realized how rare this amp was. What did I find? Very near to NOTHING! I found one that had sold at auction years earlier and one repair shop that had one in and had tried to produce a simplified schematic on the amp (most of which wasn't right). Those TWO references were it! There was a little scrap of a postage-stamp sized schematic left attached to the bottom of the cabinet that gave me about the first 25% of the circuit, and with that and the amp in front of me, I finished off the schematic. I'll post it here for anyone else who runs into this rare gal! What was wrong? Well, in a nutshell, it had to do with the fact that VINTAGE EL84/6BQ5 tubes had pins one and two internally jumpered and "NEW" EL84/6BQ5's do NOT. My next blog will focus on this! For now, let's talk about this amp!
Here is that nicely laid-out chassis. This is after I had replaced all out of spec resistors and the filter caps. I actually found this easier to work on than a vintage Fender!
Okay, now would be a good time to talk a little about the BIGGEST mystery concerning this amp: who made it? "Kent" was a name/brand only, just like Silvertone or Airline, they never actually manufactured anything. There is a fair bit of info available on Kent guitars. It is widely agreed that the Japanese manufacturer Guyatone (aka Tokyo Sound Co.) made the vast majority of Kent guitars; Kawai, Fujigen Gakki, Teisco, Matsumoku, and even Hagstrom also made guitars that wore the "Kent" name-plate. But what about the Kent branded AMPS? Well, ummm, I just can't really say much! I sincerely hope there will be some folks who read this blog and can post some info ... seriously! All I could find is that Guyatone ALSO made Kent amplifiers. But take a look at this panel-shot "MADE IN USA"! Hummm ... made by WHO in the USA? The chassis kinda-sorta looks like a Valco, or maybe Danelectro build ... but not quite. Power & output transformers are US made as are the pots and caps, so it's safe to say it probably really was made in the USA. Again the question: by who?
Okay, where the rubber meets the road: how does she SOUND? The short answer: pretty cool. But hey you are TONE-SEEKERS ... you want the loooong answer, right? Well, when you think a pair of EL84's and a pair of 12ax7's on a tube rectified amp with tremolo it's hard NOT to think of the 18-watt Marshall ... this ain't that. The trem is VERY Marshall like ... but from there it gets wierd. You see, even though it was way outta vogue by 1965 (the date on the schematic), this amp features a grid-leak bias on V1, what that means is that the input stage is fairly wimpy and quite ratty when over-driven. Another key difference is that the Kent runs a very conservative 260-volt B+, whereas the Marshall runs a healthy 340-volts, this means the Marshall has a lot more volume and especially clean headroom. I will make a side-not here: I did substitute an actual 18-watt Marshall power tranny while I had her on the bench and, yes ... she DID sound a lot better. At some point I might consider making that transformer a permanent replacement in this amp and, along with changing V1 to the more modern/conventional cathode bias, well then ... shoot ... it WILL be almost exactly an 18-watt Marshall! Why didn't I just go ahead and do that? Well, because this amp actually DOES have it's own distinctly cool retro garage rock sound. When played through my shop speaker (a WGS ET90) it actually sounds downright addictive!
That brings us to this: What mods WILL I do to the amp? Y'all know me! I GOTTA make some changes :-) And here they are. First, you will notice that there are THREE(!!) inputs, ant they are all exactly the same. They are voiced exactly alike. What? Now, with the grid-leak bias on V1, there is a cap that couples the input to that first tube stage ... and it's VERY important ... shoot, it voices the entire amp! (Note: see schematic below) The factory value of .05uf was fine with single-coils and with the volume kept low and it probably worked just perfect with the low output pickups of the Kent Polaris guitar, and during a time when folks tended to not push an amp into distortion, but ... with modern humbuckers and the volume dimed, it was pure elephant farts! I found that the MUCH lower value of .005 was excellent when fully cranked, and the mid-way value of .01 was optimum for slightly over-driven settings. So, my first thought was "I'll wire each input jack with each of the three values". But, plugging in and unplugging to change tone wouldn't be very convenient on-stage. So, I plan to use one of the three input holes to mount a three-way switch and I'll lable the three positions "FAT", "TIGHT", and "Bright". How cool will that be? and ... it'll still leave me two freeking input jacks!
And one last thing: You guessed it ... THE SPEAKER! Gang, this one is going to blow your minds!!! Now this cabinet looks like it probably houses a 12", or maybe 15" speaker, but NO ... it has a single 8" speaker! Not Kidding!! I've always lamented the fact that manufacturers skimp on what matters the MOST (Speakers in amps and Pickups in guitars) ... but never have I seen the situation taken to this extreme. This poor little 8" was good for about 10-watts absolute max, and even with the low B+ voltage, this Kent was capable of an easy 14-watts (more when driven), plus, it just sounds tiny! What on earth were they thinking? So an upgrade is obvious, but what? Ya all help me out here! I'm thinking I might go with a G10C and a G8C ... or maybe THREE G8C's (yep, they'll fit) ... or maybe a single 12 like the G12Q ... or maybe even a G15A. Tough decision!
Next Week: I'll explain in detail that little pin 1/2 issue with EL84 amps. Folks, if you run an amp with a pair of EL84/6BQ5's ... you will want to know this! See ya then!