M Fowler wrote:Thats because we put the amp in front of us in those days and plugged in our guitar and mic to the amp.
On some gigs there was only one amp shared by bass, guitar and mic. No accordion in my bands, not that I didn't like them.
The first PA with monitor if you will.
I'll tell you this much those old tuck and roll ss Kustoms sure didn't like 2 guitars plugged in and turned to 10. Blew up one after the other. Oh, to be a kid again.
Once I get this Harvard built I will have to try Mic, Guitar and Accordion in all 3 inputs, I'll report back
rp wrote:I really want to build it with just 2 inputs, I'm sure the choice of 3 was the Sales or Marketing dept looking for something to help the salesman explain the Harvard next to a Princeton and Deluxe - "Well sir, this one's got three inputs!" But for all I know Cropper plugged into the odd one (#3?) so I'll build it straight. Plus it will be a 'coolness' test, it's going into a ss Marshall 10" carcass, so anyone in the know will be tipped off by the 3 inputs that it's a Harvard.
I already mentioned the tweed Vibrolux similarity to the Harvard. Both of those have three inputs. The 6G2 brownface Princeton is really close to the Vibrolux, but some changes in the trem oscillator and two inputs instead of three. You could still keep to the 6AT6 and just steal the two input configuration. At least for breadboarding, it'd be interesting to see how differently the circuit behaves with the input circuit change.
Used to be that the guitar controlled the amp, vol., tone, the volume pot. on
the instrument determined the impedance, but you got a grid wire from hell
so the input resistors are more as stoppers.
Another way to argue it, It looks like a transition from a zero bias or grid leak.
I had a havard over the bench last year, nice little thing all original parts.
It has its own tone because of the input a first gain stage, 5f10, still had
its original selenium rectifier, the thing presented like a princeton.
I like trying old fashioned ideas, that input is pretty common for low dollar
consumer product of the time, more than one input was a sales point.
These amps were the PA for the entire band, vox, accordion, and guitar.
Well, it's built and running well and getting dressed for it's AG debutante cotillion. I got a problem with the inputs. They look pretty good to me, and 2 & 3 work perfect but 1 (high) buzzes and hums real loud as if it's ungrounded. I even tried adding the 1M load resistor thinking that was the problem but no luck. Here are pics, maybe someone will see the problem I'm stumped. Could the jack be bad? The series R on it?
You do not have the required permissions to view the files attached to this post.
martin manning wrote:Looks like it's wired correctly. Are you sure it isn't a problem with the sleeve contact in the #1 input jack?
I was hoping you'd reply Martin. Beats me, it's a new Re'an. I don't think I have much choice but to replace it and the 68k and see if that's it. Bit of a bummer as it's all nice and clean. And while anything is possible it's 99.9% unlikely it's a bad jack. Hmmm, guess I can alligator jumper onto it and clip on the guitar cable. That would answer the defective jack. BRB.
martin manning wrote:Looks like it's wired correctly. Are you sure it isn't a problem with the sleeve contact in the #1 input jack?
And while anything is possible it's 99.9% unlikely it's a bad jack. BRB.
That .1% will get you every time! Bad jack. There's always something.
What's really odd is that inserting a dummy plug into the jack to disconnect the switch does lift the switch but somehow doesn't connect to the shield, pull the dummy plug and no sound (switch works). The super weird thing is these jacks disconnect the switch by pushing up the shield - ie making contact. WTF? Guess I will find out when I pull it.
OK, I replaced the jack and that's not it. It has got to be my wiring. So far: hum/buzz when plugged straight to 1 in but works fine when jumpered. 2 &3 ok.
as the plastic can and will melt if you linger to long.
Tom, I know, it's why I'm getting irked, besides my saturday. I hate the look of melted ugly plastic mishaps in my amps. My re'ans are gonna get ugly fast. The 2 working ones are also reused and look it. I also have few left and the cliff are a little different in size.
The amp's looking 100% except for this.
You do not have the required permissions to view the files attached to this post.
First off, your thread (when first posted) inspired me to study my two Fender builds, only to find out that I had wired the 5F6A inputs incorrectly. The 5F6A needed switching jacks which I threw in so that I now have the appropriate pairs of inputs. So thanks for that .
My 5C3 build has a similar problem. When I'm using the first input (two inputs tied together) everything is good and dandy. But when I use the second channel, I get some random AM radio and occasional sputters if I stand in the right spot. From what I can see the soldering itself is fine so I think I need to just redo the input section for the second stage (move the grid stopper closer).
Have you tried ohming everything out to ensure continuity? Plug in the first jack and leave the other end unplugged. Should measure 1 Meg from tip to ground.
Martin, correct, your drawing and my layout match.
Cliff, glad to oblige. My 5F6A was one of the first amps I built (pre-internet) I had the inputs wired wrong in it for years, before I figured it out. I did your test, pics below.
- Open when clipped to the plug - pic 1
- I get 1M when clipped on the jack - pic 2
- 1M when clipped tip to the plug, but shield to the jack - pic 3
WTF???? Dang I'm way puzzled. Two bad jacks??? My head hurts. Been at this since I got up. I'd walk away if the amp wasn't otherwise 110% and sounding amazing.
BTW, the 1M load resistor is just clipped in for testing. The orig design omits it. I tried it both ways, and it makes one hell of a difference. The amp is just blistering without it especially #1. Once I solve the input problem I will test this some more.
You do not have the required permissions to view the files attached to this post.
So the first jack is known to be good? Each jack should read 1 Meg when referenced to ground! If all three 68k resistors are in parallel then you just need one 1Meg to ground to get the intended effect of this resistor..
Ohm out the resistor and make sure it's not open. Is it making good contact to the jack?
My first build was a 5F10 done with ALL 7-pin tubes. I found with a 6AT6 in V1 that any HB guitar would just blow you straight into major overdrive territory, let alone a 6AV6 in that position.
So I looked in RC-73 for alternatives, the 6a*6 is a bit like the 12A*7 in that there are different mu versions available, and got some 6BF6, mu=20. With a 6BF6 in V1, you have some serious clean tones possible, in fact you need a pedal to get any heavy overdrive. That 6BF6 is still in V1. Try it you might like it. Or you can put a 6AV6 or 6AT6 in V1 and a 12AT7 or 12AU7 in the PI (change plate resistors for those). Lots of possible options!
My build wasn't exactly a clone, besides all 7-pin tubes I used two 6X4 rectifiers in parallel and Mercury Magnetics iron, all of which helps to clean up the tone and give it a little more headroom. If I pulled one of the 6X4s it would really sag bigtime, if that's your bag. If you build yours with two 5Y3GT in parallel you have the same option.
.