just bought this,EVEREADY SKY QUEEN valve/tube radio, going to try and turn it into a guitar amp, never worked with valve's before so there'll be lot's of question's, started unsoldering everything at the moment,

 

Views: 7891

Replies to This Discussion

very cool fella.  do you have a schematic of what's there?  if not, i would try to trace through the wiring thats there to work out the connections to the transformers if nothing else.  this should tell you which conections are for the heaters, and which for the HT etc. if you can still read the markings on the valves, look up their pin-outs (google 'tube database'), and trace back to the trannies.  at least 2 of the valves you won't have to worry about (radio valves - usually have odd looking screens inside the glass). 

you are looking for the rectifier tube, power (amp) tube and a pre-amp tube.  the connections to these three tubes should tell you all you need to rewire it.


good luck!

I've done one, with a LOT of help from an electrical engineer buddy. 1) Be careful! There's a lot juice running around in there. 2) In my case, and I suspect with a lot of the valve radios, the tubes are pretty weak. We're going to mod it to turn one of the non-amp tubes into an extra gain stage.

I think some people are pretty much gutting them and putting a proper tube amp for guitar inside.

if the marking on the chassis is right, the EL90 is the power tube, and although it's a mini 7-pin, on paper it puts out very close to a 6v6 - about 4.5W.  You might have yourself the makings of a fine champ there.

tube data link here...

http://tdsl.duncanamps.com/show.php?des=EL90

been reading up on tube amp's and have come up with this circuit, it's probably wrong, cap,resistor value's etc, if someone can help me out and correct it i'd be very gratefull, 

looking good fella.

just had a quick look and seen a few things.

you won't need those two diodes from the power trans to the 6X4 - that's what the tube is anyway.  i would probably run a stand-by switch where you've drawn the diodes, but not vital with a tube rectifier.

your grid input of stage one needs a ref to earth to bias properly, so put a 1meg resister from the hot side of the jack to earth before the 47k res you've shown.

your 2k2 cathode resistors are pretty large, but that might be what you need to bias the 6AT6 - you could draw the load lines up off the data sheet and work out the sweet spot for the tube.  i would also bypass the cathode resistors.  caps could be anywhere from 1uf to 25uf (25v) - this cap will affect the bass response and can tidy up some ugly distortion when cranked.

i would recommend a grid stopper resister on the EL84. solder it right at the lug on the socket. maybe 5k6? this will help to make the distortion sweeter when driving the power tube hard. and can be required sometimes for stability.

i would also bypass the cathode resister on the EL84 with a 100uf cap (50-63v). the feedback from a cap here does reduce your gain, but will give you far superior tone IMHO.

other than that, it looks good.  measure all your voltages once you arc it up, and check everything is as it should be. i always like to calculate the actual current through the power tube too. just to make sure that's all good too.  max plate disipation for the EL84 is 12W.

i assume you are changing the power tube from the 7-pin EL90 in the original amp to an EL84 as in your schematic. the load for the output trans should be fine, but bear in mind that the EL84 uses a bit more heater current - 760mA vs 450 mA.  i would add up the heater current of all the original tubes just to see how it compares with your new load.

have fun, be safe, let us all know how it goes!

e

thank you very much for all that information, i'm still a newbie at all this tube stuff, so i'll have a few question's about the info in your reply,

but for now,

the ss diode's (1N4007) are insurance in case the rec/tube short's out, they protect the power transformer, so i've been told, they only cost penny's and only reduce the B+ voltage 0.6v, so it sound's good to me,

i'm using the small chassis from the radio and OT, 2- 6AT6 (in place of a 12AX7A), EL84 and a 6X4 rec, i bought a used PT that has all the output tapping's i need, 300-0-300, 2 x 6.3v heater supply's, so i'm ok there,

the circuit i've drawn is bit's and piece's from other circuit's, as i've not seen a circuit using 2- 6AT6's, so i'm unsure of the value's of the resistor's and cap's, what i cant figure out is how do you know when to use an electrolytic  cap or say a poly or ceramic cap in the circuit,?

when you say "bypass the cathode resistor on the EL84", what do you mean, put the 100uf cap in parallel with the resistor,? more question's to come, thank's,,

the diode thing sounds fine, although i've never seen a short here blow the trans.  the fuse on the mains side of the trans should blow anyway. and yes, the tube rect will drop way more voltage than the silicon blobs.

as to cap type - for some placements it depends on value/size to a large degree as well as purpose, different types of caps aren't available in all values. wilth the smaller value caps, there are multiple options, with potentially minor tonal variations. usually electrolytic (polarised) for power supply and cathode bypass caps.  600v rated poly-something caps for coupling.  i avoid ceramics personally, though lots a vintage stuff used them - if you stick in a single pot tone control you may need one.

yes, bypass the cathode resistor means to run the capacitor in parallel with it.  i had it ass-about in the previous post, and the cathode resistor actually creates neg. feedback, reducing the gain of the stage.  the bypass cap blocks AC and gives you back the gain the resistor took away. BUT this cap in conjuction with the internal resistance of the tube creates a local low-pass filter, ie. if the value of the cap is low, it will give you back your trebles, but not your bass.  anything above 10uf should give you everything for guitar, the fender standard 25uf is obviously fine.  you could use a .68uf if you were going for a bright channel perhaps.

to see what the bypass cap does, check out this calculator online.  your 6at6 fits in between a 12ax7 and a 12at7.

http://www.ampbooks.com/home/amplifier-calculators/cathode-capacitor/

e

this is the No 3 drawing, think i'm getting somewhere near for it to be ok, what do you think eric,?

the grid stopper resistor you mentioned for the EL84, would it go on pinout No9 or No2, ?

 

that's looking the goods to me. the grid stopper for the el84 goes on pin 2.

the 1M grid leak resistor on the input is usually soldered directly across the input jack too. oh, not sure if you know, but make sure you use a switching jack, not a guitar jack for the input, ie. the input line is earthed when you pull out the guitar lead.

looks good, and you look ready to crank up that iron!

e

thank's for the info eric, could'nt have done it without your help, i've been itching to start soldering, but i wanted to make sure i had the schematic right before i started, and also trying to understand how a valve and valve amp's work, i've gained a bit of knowledge, but i've still a long way to go, but i'm really enjoying it,

started putting a test bed together, just to see if everything work's,

 

hey, hope the build testing is progressing well. was just looking through some old schematics i have here, and found this for the fender harvard.

its the first i've seen with your 6at6, and the cathode res and cap and plate voltages for the preamp would be a good place to start for a guitar amp.  as i mentioned before, i would also put in a one knob tone control.  ones like in this circuit use no extra parts on the board - the 2 caps and the wiring all just run between the tone and volume pots. very simple, and works too.

e

RSS

The Essential Pages

New to Cigar Box Nation? How to Play Cigar Box GuitarsFree Plans & How to Build Cigar Box GuitarsCigar Box Guitar Building Basics

Site Sponsor

Recommended Links & Resources


Discussion Forum

Ruby Amp

Started by BrianQ.. Last reply by BrianQ. May 18, 2020. 6 Replies

Smokin' amp (literally)

Started by James Conder. Last reply by James Conder Aug 27, 2019. 4 Replies

Simple Headphone/Practice Amp

Started by BrianQ. May 16, 2019. 0 Replies

Problem with second-hand amp.

Started by Arthur Payne Mar 31, 2019. 0 Replies

Artec Amp Help!

Started by Jesse Lively Sep 10, 2017. 0 Replies

LM386 N-4

Started by Denis U. Last reply by Richard Haas Dec 3, 2016. 4 Replies

History Mystery--Orrtronic Tube Amplifier project

Started by Scott aka Farmer Ted Nov 17, 2016. 0 Replies

Dual IM386 Chip amp

Started by Paul Craig. Last reply by Paul Craig Nov 3, 2016. 31 Replies

Amp Speakers

Started by Primitive Acoustics. Last reply by Primitive Acoustics Mar 9, 2016. 3 Replies

Grounding for Cigar Box Amps: Chassis Ground?

Started by Erik Bell. Last reply by Scott aka Farmer Ted Dec 20, 2015. 4 Replies

Neat amp components

Started by Surly. Last reply by Alan Steeg Oct 27, 2015. 1 Reply

can a dab radio be turned into an amp

Started by Coventry Halfpenny guitars. Last reply by Pickedmoor Jon Oct 20, 2015. 3 Replies

SDA-T Questions

Started by alectron. Last reply by Zac Ray Sep 2, 2015. 10 Replies

HI - New guy & And speaker question

Started by Henry S. Last reply by Henry S Mar 25, 2015. 4 Replies

Are Pre-fabbed LM386 Moduals Worth Trying?

Started by Scott W. Last reply by Henry S Mar 24, 2015. 6 Replies

Powered sub to amp ??

Started by wormil. Last reply by wormil Sep 2, 2014. 2 Replies

Amp and speaker INSIDE the guitar?

Started by Greg Potts. Last reply by Ron "Oily" Sprague Jul 1, 2014. 1 Reply

trying to hack an old valve radio, into a guitar amp,

Started by GARAGE HERMIT. Last reply by GARAGE HERMIT Apr 29, 2014. 108 Replies

Best mini amp KITS

Started by MichaelS Country Boy Guitars. Last reply by Henrik Johansson Mar 10, 2014. 34 Replies

amp wiring help

Started by HarleyTodd. Last reply by Bernie Mango Feb 26, 2014. 18 Replies

Latest Activity

Dar Stellabotta posted a video

A Cigar Box Guitar Six Stringer Built by Louie Lamanna

This video is the unboxing and the demonstration of a beautiful, six stringer built by Louie Lamanna. Join Louie and I June 15 at the second annual Pittsburg...
37 minutes ago
Doug Thorsvik commented on Doug Thorsvik's video
Thumbnail

Hail the Resurrection Day: 2-String Violin Chugger Cigar Box Guitar

"Happy Easter to you too Andries! The passion is definitely in full swing. Turns out I’m…"
1 hour ago
A.D.EKER commented on Doug Thorsvik's video
Thumbnail

Hail the Resurrection Day: 2-String Violin Chugger Cigar Box Guitar

"Happy Easter Doug ! the Passion is in full swing !"
1 hour ago
A.D.EKER commented on Ricky D's photo
1 hour ago
A.D.EKER commented on A.D.EKER's video
1 hour ago
Keith Rearick liked Doug Thorsvik's video
5 hours ago
Keith Rearick liked A.D.EKER's video
5 hours ago
Keith Rearick liked Doug Thorsvik's video
5 hours ago
Keith Rearick liked Ricky D's photo
5 hours ago
Keith Rearick liked Ricky D's photo
5 hours ago
Keith Rearick liked Ricky D's photo
5 hours ago
Keith Rearick liked Ricky D's photo
5 hours ago

Music

© 2024   Created by Ben "C. B. Gitty" Baker.   Powered by

Badges  |  Report an Issue  |  Terms of Service

\uastyle>\ud/** Scrollup **/\ud.scrollup {\ud background: url("https://storage.ning.com/topology/rest/1.0/file/get/963882636?profile=original") no-repeat scroll 0 0 transparent;\ud bottom: 25px;\ud display: inline !important;\ud height: 40px;\ud opacity: 0.3 !important;\ud position: fixed;\ud right: 30px;\ud text-indent: -9999px;\ud width: 40px;\ud z-index: 999;\ud}\ud.scrollup:hover {\ud opacity:0.99!important;\ud}\ud \uascript type="text/javascript">\ud x$(document).ready(function(){\ud x$(window).scroll(function(){\ud if (x$(this).scrollTop() > 100) {\ud x$('.scrollup').fadeIn();\ud } else {\ud x$('.scrollup').fadeOut();\ud }\ud });\ud x$('.scrollup').click(function(){\ud x$("html, body").animate({ scrollTop: 0 }, 600);\ud return false;\ud });\ud });\ud \ua!-- End Scroll Up -->