Knight 30watt tube amp

[baddog]

Hello its me again

I picked this amp up and was wondering if anyone had any ideas on any mods. It's schematic layout resembles an old Fender Pro amp. Any Thoughts Wecome.

Thanks to everyone

[gldtp99]

This is a good one---i re-did one of these Knight 30 watters as a mostly 5e5 Fender circuit (12ax7's in preamp instead of the orig octals)---i did this one in between "serious builds" because it had been sitting in the corner and i was tired of looking at it/moving it around to get to other amps, etc.
Many players have absolutely loved this head, choosing to record with it over many "real" amps in the studio across the hall----i ended building another similar head (Hammond steel chassis and a locally made JMP Marshall-ish head cab) with 60's Knight 30 watt 6L6GCx2 trannies for the studio owner----this 2nd one has been recorded/gigged/used&abused by lots of bands for over a yr now------several players have talked to me about building them a higher powered version of this head for them for stage use after using it to record with, but no $$$$ yet so i haven't started one---i've got a few 70-ish watt old PA heads that have suitable iron for this type of amp.
I actually have another 50's Knight 93 series 30 watt 6L6x2 amp here that i haven't re-built yet.
Just make sure that you add a fuse when you re-do the power supply--- At least fuse the AC Mains and maybe the HT also-my Knight didn't have any fuse at all so i fused the AC Mains when i put in the new grounded power cord-----actually almost everything inside is new except for the trannies, 6L6 and 5U4GB sockets, and power lamp.
I had no idea that this conversion would turn out so well----this is a good old head (Art Deco looking thing) and the 5e5 Fender circuit is a great fit for it---- pretty much a Tweed Deluxe @30 watts w/6L6x2, one Vol and one Tone---what's not to like ?......................gldtp99

[baddog]

I already made 12ax7 adapters for the 6SC7 sockets. I am going to re cap the amp and try it first. I might be happy with it the way it is. Do you now if i need to change the bias for the 12ax7 when i install it. When i did a test run with the adapter the amp took a little time to warm up and it wasn't a nice smooth warm up like with the original 6sc7. Any thoughts. What size fuse did you use in the amp?

thanks
keith

[gldtp99]

3 amp Slo-Blo fuse for the Mains---- http://www.schematicheaven.com/fende..._5e5_schem.pdf

I'd go ahead and gut the old Knight circuit and rebuild using new components---- early 1950's resistors and caps, pots, old wire are not what i'd trust from a reliability standpoint.
I'd look closely at the transformer wires for degraded or cracked insulation and cover with shrink tubing if there's any doubt at all about them.
I built a somewhat later break-up version of the orig Fender circuit and i ran the halves of V1 in parallel--- only one 1/4" input jack on front panel.
I believe i used a 3.3k non-bypassed cathode resistor on V2a (only two preamp tubes in my version----V2 is the gain stage/PI tube just before the output tubes in my amp).
I set up V1 for a 12ax7 (not the 12ay7 as in the orig Fender) but i don't remember exactly how i did it---i can look if you want.
I used a JJ 40/20/20/20@500V can for filtering and a Fender replacement 125C1A choke instead of the power resistor in the orig Fender circuit and also 470 ohm/5 watt screen grid resistors mounted on the 6L6 sockets.
My Knight came with RCA 6L6GA output tubes that test very strong but i put in new Sovtek 6L6WXT+ output for initial fire-up/testing---- the amp sounds so good with these that i haven't taken them out and tried anything else yet---- a real Blackburn Mullard ecc83 is in V1----- the simplicity of this circut really lets a premium tube in V1 shine through---i tried lots of different preamp tubes but this one Mullard kills in this amp..........gldtp99

[baddog]

I really dont have the money or the parts for a total rebuild . Is their a way i can get later breakup out of this amp without tearing it apart. I am going to check all wires and replace the control wires.

thanks for the help
keith

[gldtp99]

For later break-up try 5751, 12at7, or 12ay7 preamp tube(s) instead of all 12ax7's----experiment with different gain strength tubes in the different preamp positions to get the tone response/break-up you're comfortable with.
I like to build with all 12ax7's because they are more common/plentiful.
So i adjust the circuit to use all 12ax7's to get the tone response/break-up i want.
Similar results can be achieved by using lower gain 12a_7 or 5751 preamp tubes as needed.....................gldtp99

[baddog]

If i change the preamp tube in V1 to say a 12ay7 wont that lower the volume of the amp also? Sorry it takes so long to respond i'm at work

thanks
keith

[Dave Curtis, dB AudioTech]

Changing to a lower gain preamp tube doesn't change the volume of the amp very much, depending on how much lower you go.