Looking for Knox amp info

[tonefreak]

Hi, I just picked up this Knox 1 12 combo and was wondering if anyone has ever owned one of these. tube layout is 2 12ax7, 2 el84, 1 ez 80/6v4(rectifier?)...I cant seem to find any info on this. What I'm wondering is what type of circuit this is. single ended or push pull. I dont know enough about amps to tell by just looking. Anyone?..Thanks..ohyeah this think really honks with the volume and tone dimed. also anyone know what brand of tubes these are..all are marked HE...thanks again

[steve]

tonefreak,

If I had to guess, I would say that that circuit is push pull. Can you take a picture of the transformers?

One way to tell is to find pin 7 on the EL84 tubes. If there is a different colored wire going to each tube, then the amp is probably push pull. If pin 7 from one EL84 is connected to pin 7 of the other, then the amp is parallel single ended.

Generally in a push pull amp there are three wires coming from the primary: two anode connections and one center tap which connects to the B+. Generally the colors are blue and brown for the anode connections and red for the CT, but not always.

On a single ended amp there are two wires coming off the primary: one for the anode and one connecting to the B+. Again on some OTs these wires are blue and red. However, hammond 125SE series has blue and brown.

Since parallel single ended amps are relatively uncommon, I would bet it is push pull and similar to the Marshall 18w circuit, but that is just a guess.

BTW, are you the tonefreak that used to post to the Kronosonic BBS?

steve

Hi, I just picked up this Knox 1 12 combo and was wondering if anyone has ever owned one of these. tube layout is 2 12ax7, 2 el84, 1 ez 80/6v4(rectifier?)...I cant seem to find any info on this. What I'm wondering is what type of circuit this is. single ended or push pull. I dont know enough about amps to tell by just looking. Anyone?..Thanks..ohyeah this think really honks with the volume and tone dimed. also anyone know what brand of tubes these are..all are marked HE...thanks again

[tonefreak]

I'm not sure which pin 7 you mean Steve so I'll describe it like this..
if you start at the gap between pins 1 and 9 and count counter clockwise pins 7 on both el84's are connected then run to the filter can cap then to a 7 watt resistor then to the rectifier tube.

if your counting clockwise pin 7 on one tube is connected to an orange wire from the ot....pin 7 on the other is connected to a green wire from the ot

Thanks for your help Steve..oh..must be a different tonefreak your thinking of as I've never posted there...

[tonefreak]

Hi Steve..checked out a schematic for an 18 watt Marshall and yeah your right ..Its push pull....hey I even learned something!..which pins do what..Much thanks to you and have a great day

[steve]

tonefreak,

The pins on the EL84 sockets look like they are numbered. Pin 7 is the anode (sometimes called the "plate").

From the photos, your amp looks like it is push pull. The orange and green wires coming from the OT confirm this.

I'm not sure which pin 7 you mean Steve so I'll describe it like this..
if you start at the gap between pins 1 and 9 and count counter clockwise pins 7 on both el84's are connected then run to the filter can cap then to a 7 watt resistor then to the rectifier tube.


Counting this way, you are describing pin 3, which is the cathode. The 135 ohm resistor looks like a cathode bias resistor.


Thanks for your help Steve..oh..must be a different tonefreak your thinking of as I've never posted there...

Sorry, my mistake :)

steve

[tonefreak]

Yes the pins are numbered..had to get out a magnifying glass but they are and there is an orange wire to one and green to the other from the ot so yeah its push pull.

Ok one more question if I may.

couldnt find a bias pot in this thing so im assumming bias is fixed with resistors. when I take this thing in to have new power tubes put in should I have him put in a bias pot so it can be set properly..Thanks so much for all your help

[nomadh]

I have a knox also. It has the schematic with it luckily. Unluckily I am very rusty at schematic reading. Never read one with tubes before. My Knox is a model 603 with tremolo. It has a loud hum that goes up and down with the volume but also lessens when tremolo strength is increased. Maybe all us know owners can get together and share info. So far there is nearly zero info on these amps.

[nomadh]

I played with my 603 knox amp that also has the HE tubes but mine are 12av6 12au6 and a 50c5 tube. Good news is after putting in another set of tubes it worked then the original HE tubes worked. Both had a bit of buzz or hum but not terrible for an old amp. The big problem is the farty sound. single or double coil, guitar volume max or medium. Same for the amp vol. Even lowered it still has a farty tone. Hope that isn't too technical :). So now it seems to work but not nice. I soppose it could be one of the tubes but any combination of both sets sounds the same so it doesn't seem likely but I don't have a tube tester to prove it.
I also just got another knox amp. No model number same tube lineup as above except for the addition of a 35w4. This amp has no model number and no schematic. If the other amp sounds farty this one is deep in the colon. Any knob setting gives a max vol buzz with just the barest of guitar sound coming through when you slam a power chord. Any info on this please post a reply here and I'll try and monitor this thread. Perhaps if we collect enough of us knox orphans we will have enough info to make these things work.

[dslea]

Hey, I got i Knox amp at a garage sale. the speaker is kind of jacked. all orig im guessing from 1968. I am fustrated to that there is no info on these amps. It had HE tubes. 1 EZ81, 2 6BQ5 and 2 12AX7's. It played when I got it but it didn't have alot of output. I replaced the 12ax7's with some mesa tubes I had around the house and it sounded pretty good. I would say it sounded excellent except there is some krinkling at higher volumes which will hopefulley go a way when I replace the rest of the tubes. I don't know the model. It is 2 channels and tremblo. there is a schematic. I would need a microscope to read it though. If anyone has this amp and is willing to let go of the knobs I will pay them a fail price for them. The old guy who sold it to me said some one stole the knobs.

[dslea]

Here are the pictures of my amp. If I had to guess I would say the model of my amp is DR-75. I made a drawing of the schematic thats on the cabinet. There might be some errors beacuse the print was so small. Some stuff I could not read at all.

2809

http://i243.photobucket.com/albums/ff307/danlea1/001.jpg
http://i243.photobucket.com/albums/ff307/danlea1/005.jpg
http://i243.photobucket.com/albums/ff307/danlea1/002-1.jpg
http://i243.photobucket.com/albums/ff307/danlea1/004-1.jpg
http://i243.photobucket.com/albums/ff307/danlea1/005-1.jpg
http://i243.photobucket.com/albums/ff307/danlea1/003.jpg
http://i243.photobucket.com/albums/ff307/danlea1/004.jpg
http://i243.photobucket.com/albums/ff307/danlea1/002.jpg

[nomadh]

It looks like you got the fancy model of knox. Real standard tube compliment. Even dual channel. It looks better made than mine also. Maybe between 14-18 watts. I think my amp is less than 6 watts. One of my amps has knobs like yours but they have surface rust. You amp may be a much more standard design than mine.