Thanks for the pic Doc, the wiring looks to be of an "interesting" standard.
From pics on the net I Don't Think Fender Done It This Way ( apologies to Waylon )
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Thanks for the pic Doc, the wiring looks to be of an "interesting" standard.
From pics on the net I Don't Think Fender Done It This Way ( apologies to Waylon )
Quote:
Originally Posted by dave.king1
Granted it does look a bit like a "rat's nest", I might see if I can tidy things up when I get round to doing the restoration work on it, the chassis definitely could do with a bit of a clean-out and service, I did spot one electrolytic cap that looked like it was on the way out.
Update:
Did some googling for schematics for the Fender Super Twin and found that what I actually have is the non-reverb version, apparently there are two Super Twins that Fender used to manufacture, there's the Super Twin Reverb which uses a couple of unusual valves in the preamp, and then there's the Super Twin non-reverb which uses the same preamp circuit minus the reverb circuit, but is basically the same as the Super Twin Reverb, so, going by that, it's most likely that my Super Twin amp hasn't been modded but has had some electrolytic caps replaced, I haven't had a look inside the metal cover that's covering up all the main supply filter caps yet, this cover is sometimes referred to as a "Doghouse" by amp techs, this coming fortnight, I'll see if I can order a replacement Fender style knob for it and some new valves for my Legacy amp from Evatco.
OMG !!!.... Been a way long time since I've had to work on gear that looks that untidy, along with much fear that anything you touch might disintegrate...lolQuote:
Originally Posted by DrNomis_44
... Probably doesn't look as bad in the flesh, but the photo sure brings out the worst of the cosmetic aspects of it...
Quote:
Originally Posted by Marcel
But in a funny and perverse kind of way, the insides of the chassis seems to be what really gets me excited, I guess old school electronics fascinates me for some reason that I don't quite understand.....lol.
I know where you are coming from on that...
There is a simplicity and a danger in tube gear that solid state just doesn't have. When you think of it nearly all tube gear gets their results with typically less than 10 active elements. Some how I think, and regardless of how it may sound or cost, we will never see the day where a solid state 50W 2204 style amp will ever be released boasting only 8 transistors.
Yeah, the danger is all pretty much the high voltages at potentially lethal currents. 500VDC @ 300mA in a guitar amp is more than enough to switch off a human life... and if working on that gives you a 'buzz' then maybe old school AM radio broadcasting repair might be worth a try where 6kVDC @ 700mA is quite common and 25kVDC @ 1.5A over two serious power tubes in series is often encountered, The thoughts of working anywhere near those voltages make some break into a severe nervous sweat, whereas others like myself it is our day-to-day job ... go figure...
Regardless of all that my heart just loves hearing a good tube guitar amp. 2nd harmonic and even overtones sound so much better when produced by real tubes than the filtered third and odd harmonic overtones that are the more natural condition of solid state. I suppose it is all a question of balance really....
Quote:
Originally Posted by Marcel
I think part of my fascination with Tube/Valve technology is that I'm tired of trying to work with components that require a magnifying glass and a pair of tweezers just to read the component values and solder them onto circuit boards, I prefer working with components that I can easily hold in my hands and read without squinting my eyes, I've found that in reality, surface-mount devices are not more reliable than conventional components, but if other people like SMD technology well then each to their own.
When a Valve amplifier distorts, or is overdriven, as you have said, they do generate even order harmonics, and they definitely do sound more musical, to my ears the difference between an overdriven Valve amp and an overdriven Solid-State amp shows up as a high-frequency crackling when a Solid-State amp is overdriven, a Valve amp sounds a lot smoother to my ears, it has a fuzziness in the high-frequencies, plus the distortion harmonics tend to be mostly in midrange and upper midrange frequencies, but the overall tone is more determined by the circuit-topology of the amplifier, my Marshall MA100C is an all Valve 100 Watt amplifier and the signal-path is all through Valves from the input through to the output, there is some solid-state circuitry but that's mainly for channel-switching, reverb, and the resonance control which affects the low end in the amps power-amp section.
And it's true, for a basic Triode gain-stage you need less passive components to get it working correctly than you need for an equivalent Bipolar Transistor gain-stage, you only need three fixed resistors to get a Triode gain-staged biased correctly, whereas a single Bipolar-Transistor needs four, yes there is the Fet (Field Effect Transistor) which is like a Solid-State equivalent of a Triode, but in actual fact, the Fet behaves more like a Pentode.
If you do know what you are doing and follow the correct electrical safety procedures then Valve amps can be safe to work on, provided that you keep your head screwed-on.
Amen to everything you wrote Doc...you are preaching to the converted...lol
All my tube knowledge basics (and a lot of what I know about electronics) I learnt back in the early '70's. To get out of the Melbourne winter cold I joined the schools ham radio club. It is amazing what sinks in to a young teenage mind when you overhear doctorate professionals giving an in depth Amateur radio training course on the subject at a time when tube technology was still regarded as 'current' and the 2N3055 and the NE741 were the new kids on the block...
As for SMD.... try playing with that stuff on 10GHz or 15GHz where true 'White man magic' starts to happen and everything below 1GHz seems to behave like DC by comparison ...
I have similar to you with my JVM210c. 100W 2x12 combo with bucket loads of gain on an all tube signal path and solid state switching and digital reverb. It is certainly more amp than my meagre guitar playing deserves...
Quote:
Originally Posted by Marcel
I've been into Electronics as a hobby since I first started when I was 13 years old, I'm 47 years old now, turning 48 in August this year, I'm mostly self taught in Electronics but I did do some formal studies in the mid 90's at my local University, I've got lots of build projects in my head that I would love to do, you may have seen my DIY Valve Amp Head thread in the Pitbull Guitar Amps section, haven't been able to order the bits I need to do some more work on it this year so far, had other things I needed to put my money into, but hopefully later on this year I'll be able to do more work on it, I do happen to have some test equipment like a Signal Generator, a good 20Mhz Dual-Trace Oscilloscope, some good Multimeters, a couple of good temperature controlled Soldering Stations, but I'll need to design at least one good Dummy Load for testing/biasing guitar amps, this whole Electronics hobby thing is a fun learning experience, and so far I've enjoyed it a lot.
One thing I would love to learn is how to design a good sounding speaker cab for musical instrument amplifiers, I've got a great book lying around somewhere that's got all the theory and stuff in it about designing speaker cabs, it's mostly geared towards Hi Fi speakers but the underlying principles are the same, the book is written by a guy called Vance Dickason, and you can buy it from your local Jaycar Electronics shop, I've got another book called Build Your Own Audio Valve Amplifiers, which is written by another guy called Rainer Zur Linde, Jaycar Electronics also sell this book, it's mostly geared towards Hi Fi Audio Valve Amplifiers but there is a section on Guitar Amplifiers in it too, there's also a great project for a Stereo Hi Fi Valve Preamp and there's also PCB artwork included too if you want to etch your own PCBs, pretty cool, I'm seriously thinking of building one one day once I can get all the parts I need, other pieces of Valve equipment I'm seriously interested in building are a set of four Gyraf Audio Valve Preamps for my little bedroom studio, but I need to source some Lundahl input and output transformers for them first though, and they are not cheap.
Here's a link to the Gyraf Audio website, some really cool stuff on it:
http://gyraf.dk/
The Gyraf Audio Valve Preamp I'm interested in building can be found amongst the DIY projects, it's called the G9 Mic Preamp.
Wow... lots of good stuff on the Gyraf site... And that G9 preamp would be quite fun and challenging to build...
Much the same here... Got into radio in year 7 by joining the school radio club in '73. Radio tech in the RAAF until '86, Roadie work for a while and played Audio tech at Brisbane Expo 88, Wanted a real job so worked as a tech for radio and TV stations then moving on into aviation electronics for a few years, now after collecting all the tickets and licences I need to hold I'm back as private contractor tech for commercial radio... I'm 55 now and collected heaps of junk and test gear over the years that all sits gathering various amounts of (wood) dust in my 9mx12m shed that also doubles as my luthery workshop that was setup mostly to help recover from a heart condition...lol
It's all good.... Like everybody, I know a bit about some things and not much about others...
He he I hear you with that last statement Marcel. I know enough about Electrickery to get myself in trouble and have become wise enough over the years to know when to stop fiddling to avoid real trouble.
I hope the ticker troubles are behind you now.
I saw my local GP last week to go over the results from my most recent CT scan, and in his words "What ever you are doing keep doing it!" and he then promptly wrote out an Okay to go back to work.... So I figure I'll keep building guitars in my spare time ...lol
Good to hear its all okay, and that you can go back to work. Just not working too hard eh ;)
@ Marcel That's good to hear mate, last time I had my blood pressure measured the Doctor said that it was fine, and the last time I had my eyesight tested by an Optometrist they said that it wasn't deteriorating, technically I should be wearing my glasses as I was born Short-Sighted, but I can actually see well enough without them to be perfectly able to cross the road safely.
6 months ago I collapsed in a exhausted heap after taking a simple regular shower. They subsequently diagnosed me with what amounts to a DVT in my chest right next to my heart.... so for the past 6 months they put me on a controlled and monitored diet of modified rat poison which surprisingly has actually worked to clear the DVT. Side effect has been to turn me into a real Aussie bleeder so playing with sharp knives has been a no-go for me. The upshot of no pointy knives means I've become a real whiz at cutting almost anything with side-cutters...lol
What this thing 'hard work' you speak of ??? ... Is it something you dream of ???
Lately its been my recurring waking nightmare...Luckily I have guitar building to occupy my brain with more pleasant things.Quote:
Originally Posted by Marcel
Speaking of hard work made easy...
Have you ever considered getting an amp kit from these guys Doc??
https://www.tubedepot.com/t/diy-central/kits-tube-amp
Quote:
Originally Posted by Marcel
Yep, been seriously wanting to order a JTM45 kit from that company for a long time, just haven't been able to get together the money for one, maybe that might be a good project for next year, I'd either go for the JTM45 + or the JTM45 combo kit, the other kits look really nice too.
My preference if I had the spare money to get one is for the British 18W style combo. Has a pair of EL84's on the output and comes with a Celestion G12M Greenback... My kind of combo ...
Not keen on their JTM45 kits as they have made changes to their kit circuit which are not in the published Marshall designs. I suppose the changes could be undone but as I already have my 2204 clone build the desire has waned substantially.
Maybe it's just me but I prefer the British EL34 or EL84 grunge sound over the American 6L6 or 6V6 cleans. Probably why I have built my 2204 clone and own a real Marshall JVM210c, and only ever fixed other peoples Fender amps.
One of the thing that needs doing to my Fender Super Twin amp is that the sockets for the six STR 6L6 Valves need replacing since they seem a bit loose, or the valve retainers seem loose anyway, I could go with a set of Ceramic Octal sockets with Spring-Retainers, the sockets for the preamp valves could either be kept or maybe replaced with new Ceramic 9-pins too, I might just go the whole hog and replace all the original sockets with new Ceramic ones as a matter of course, the power and standby switches definitely need replacing as they tend to stick a bit.
Seeing as I have a Marshall amp and the Fender Super Twin, I've got an amp with EL34 valves and an amp with 6L6 valves, the best of both worlds so to speak, I found that I'm mostly an EL34 guy, but, having said that, I'm not afraid to show my appreciation for the 6L6 sound, variety is the spice of life, my mate reckons that with the two amps I have the two basic food groups of tone.
Also I just remembered that I have a spare 6V6 valve in a white box somewhere, I'm thinking of pairing it up with a 12AX7 valve or a 7025 valve and making a DIY Fender Champ at some stage, I'd probably need to source a good 5Y3 Rectifier valve, or go with solid-state rectifiers, seeing as Evatco sell valves and other amp parts, I might be able to source a good 5Y3 from them, anyway, that's a future project.
I could even go with a 5U4GT rectifier too if I could source one.
There are heaps of places to get bits there Doc.
I find Ebay is often quite reasonable, but sometimes you do need to do some hunting around... For most electronic bits I usually try these Australian Online sites first...
RS components - http://au.rs-online.com/web/
Jaycar - https://www.jaycar.com.au/
Element14 - http://au.element14.com/
The two Ebay sellers below I have bought from have been quick delivery and have a reasonable variety of stuff. Think both have 5Y3's in stock..
Vicmazz - https://www.ebay.com.au/sch/vicmazz6...1&_ipg=&_from=
Amptubes - https://www.ebay.com.au/sch/amptubes...1&_ipg=&_from=
There are plenty of others (mostly Asian) that have similar and often cheaper stuff however often they only sell in quantities of 100 or more. That's way too many tube sockets for my needs... one site I got 3 Chinese made 12AX7/ECC83's for AU$32 which is pretty damn cheap.
I'm keen to build a EL84 amp... something akin to a Vox AC15... but that will have to wait until I get all my guitar builds done...
Update:
Went to my local Jaycar Electronics shop today and bought some red and black coloured banana plugs, some red and black alligator clips, and some red and black wire, these are for making a set of new test leads for my ESR Meter and the component tester on my 25Mhz Dual-Trace Oscilloscope, I think I'm going to be needing them when I finally get round to doing some servicing work on my Fender Super Twin amp, will be making the new test leads tomorrow.
Don't make your ESR leads too long. I've found 10cm to 15cm is usually plenty long enough. This is especially true for your capacitance meter as the stray stuff from leads will give you wildly false readings on the smaller value caps.
Quote:
Originally Posted by Marcel
Good point, although it's probably not going to affect the component tester on my 25Mhz Dual Trace Oscilloscope, it's one of those old school ones with a Cathode-Ray display tube in it, the component tester in the Scope uses the X/Y function to draw a straight-line, or elliptical shape on the screen for a basic go/no-go test result display, it's good for quickly testing semiconductor devices out to see if they're good or not, I'll post a pic of my Oscilloscope later on, but yeah I'll keep that in mind, cheers mate.
I have a hand held LC meter which I use to check various coils and caps. You have seen it in earlier photos.
I also have a set of 10cm leads for it for the bigger stuff, plus a very useful and accurate little PC board with 2 pins spaced the meters terminal width apart and a slot cut between the 2 copper halves so I can check surface mound bits. It gives accurate measurements as it has near zero lead length.
Update:
I've been doing some testing of the original preamp Valves that were installed in the sockets of my Fender Super Twin's chassis, I tested them by plugging them into the 9-pin socket of my Baja Real Tube Overdrive pedal, and also the preamp sockets of my little Legacy 5 Watt valve amp, one thing I did notice is that they all sounded a bit weak in gain, taking into account that the 12AT7 and 12AU7 are lower-gain twin triodes, so, I'm assuming that they are all getting a bit worn-out.
I've had a look through Evatco's stock of preamp tubes and have decided to go with a set of new JJ brand valves as replacements for all of them, here's a list of the stock preamp valves and their replacements:
V1: 7025, being replaced with a new JJ 12AX7/ECC83S Gold Pin.
V2: 12AU7, being replaced with a new JJ 12AU7/ECC82.
V3: 7025, being replaced with a new JJ 12AX7/ECC83S Gold Pin.
V4: 12AX7A, being replaced with a new JJ 12AX7/ECC83S Gold Pin.
V5: 12AT7, being replaced with a new JJ 12AT7/ECC81.
I may even go ahead and replace all the original valve sockets too, the sockets for the six 6L6 power valves do seem to be a bit loose, so maybe a set of new ones will do the amp some good, might also get some new spring retainers while I'm at it.
Might also be worth having a look under the doghouse cover and see if any of the supply filter caps need replacing with new ones.
any pics please Doc?
Quote:
Originally Posted by Guvna19
You mean pics of the amp?, I've already posted some in this thread a few pages back.
I'd have thought you'd build yourself a little tube tester in a die cast box to confirm or deny your tubes, but I suppose the Baja pedal does the same thing.
As most measurements would be DC based they can be pretty simple fixed resistor units with banana sockets for metering points. A fixed self bias for the smaller tubes maybe with a optional capacitive audio in/out is easy to implement, Larger tubes are an issue for current draw and fixed bias but it's not beyond the realms of possibility if you use reasonable sized VA transformers.
On the subject of transformers I am considering a purgatory pedal build powered by a 12VAC plug pack and having a 240:12V 3VA transformer to create the HT which I calculate should be plenty for one 12AX7, so using similar for a test box should be easy.
Quote:
Originally Posted by Marcel
I would have built myself a Tube Tester but unfortunately i don't have the parts needed nor the money to buy them, so I used my Legacy amp and Baja Real Tube Overdrive pedal as the next best things, i must put building a Tube Tester on my "to do" projects list.
Yep, It's funny how we have nil problem on spending a few hundred of the hard earned on a new guitar or a new set of wheels or a few bottles of our favourite plonk, but diverting a fifty to some useful test equipment is 'a big decision'.... I know that problem well, and have the T-shirt... ;)
Quote:
Originally Posted by Marcel
Yep, since I'm a pensioner my fortnightly budget tends to be pretty tight too, so I can only buy things when I can afford them, fortunately my big purchases for this year have mostly been done, I've got some big purchases to make next year too, need to buy a replacement TV cause my 42 inch LG Plasma Screen TV no longer powers up, and my LG Blue Ray DVD player appears to be malfunctioning too, had to buy a replacement remote for it only to find that it doesn't seem to be responding to the remote, it also occasionally displays an error message too.
When I got offered the Fender Super Twin amp for $300.00, I thought that the offer was too good to refuse, since to buy one on eBay or somewhere else would cost me way more money, so naturally I couldn't pass it up.
I did a search on Ebay and only one USA version (110VAC) is listed for five times what you paid. Everything else listed is just parts... Damn expensive parts!!
From my cloudy memory (the joys of age I suppose) most of the amps I worked on were Fender twin combo's and a handful or so of VOX amps. Even though back then I was a authorised Marshall agent in a workshop above a Brisbane Marshall store (walking distance to the Roxy in the Valley) I had very few Marshall's cross my bench, so I'm guessing the 'other tech' in Paddington got most of the Marshall work as he could hot-rod them whereas as and agent I wasn't permitted. The other guy was the Fender agent so I got to hot-rod all the Fender amps...
I'm gathering you are still mid way through the twins 'repair'...?
Quote:
Originally Posted by Marcel
Actually no, I haven't even started working on it, still in the "planning" stage, I did make some progress on the 4X10 speaker cab though, I was doing some browsing through Evatco's stock of Jensen speakers a few days ago and came across a likely candidate for a Jensen speaker to put in the new cab, it's this model:
https://www.evatco.com.au/jbb10-100
I figure that four of them wired in series-parallel like a Marshall cab should effectively give me an 8 Ohm 4X10 cab that's rated at 400 Watts if my calculations are correct, the only kicker is the price of the speakers at about $339.00 each....(yikes!), I really want to go with a set of four Jensens cause I think the amp deserves them, although I could go with Eminences or EVs.
You suffer from the same syndrome as me...always want the most expensive one.... lol
There are plenty of other Jensen's at Evacto for a lower price, and a lower wattage. I suppose it depends on how much you desire that 400W capability.
Are you building a sealed or open back cab for your 4x10's?
My 2x12 cab has a V30 at 65W and a G12H75 at 75W with both 16 ohm speakers wired in parallel to give me a 8 ohm cabinet that can handle better than 100W which is all I figure I'll ever need. Two 16's in parallel is brighter than two 8's or 4's in series, plus there is a redundancy aspect of a parallel cab and I like the sound of the Celestions so that's my reasoning for going that way.
Quote:
Originally Posted by Marcel
Yep, I want to build a sealed-back 4X10 speaker cab for the Super Twin.
Update:
Was doing some internet browsing and found this web page, the Fender Super Twin amp you see in the pic is same like the one I have, so if it makes a great bass amp then I'm keeping it for sure, it was a keeper for me anyway though:
https://www.talkbass.com/threads/fen...s-head.452093/
Very nice...
I have a feeling in my gut that says your Eminance loaded 4x10's won't sound the same as the dude's JBL loaded 2x15's.... just sayin... ;)
I prefer 10s for bass as they are usually tighter than 15s or 18s and don't flub as much.
Having said that we are different and seek our own sound, so what ever rows your boat.
Given that decent speakers cost a bomb I be trying to scam the use of a few alternative speaker combinations before draining the piggy bank
Are the valves readily available?