5E3 Chinese kit

[Geobee]

Hi all, down here in Aus, we don't have access to the great amp kits that you do, so we are stuck with a limited choice, hence the Chinese kit I am building. I have been around solid state amps for over 40 years, but limited on tubes. I am confused regarding the schematic supplied with this kit, being the wiring of the rectifier tube. From the mains transformer to the 5Y3 pins 4&6, all good, but It appears that pins 2&8 are linked going out to the standby switch ? Also, the 5VAC winding says to go to pins 2&8 of the Copper cap octal socket when using a 5Y3GT? I cant see why you would short the 5 volt winding and connect them to the HT pins of the rect tube. I have attached the circuit supplied with the kit to show my concerns.
I don't wish to build it from this schematic until it is confirmed as correct. Maybe there is a more accurate schematic that I could use/trust. Also, I assume that all thr arrow symbols are ground connections, different to the solid state ones I am familiar with. The output tubes (6V6GT) appear that the glass is blacked out, not clear, would this be normal for these tubes, just looks strange. Any help on this one would be great. Regards. Geoff

[wyatt]

Your kit suppliers "borrowed" and altered the schematic from Weber Speakers and just blanked out the company info.

Weber uses Copper Caps, plug-in solid-state rectifiers designed by Ted Weber to mimic the voltage drop of real tube rectifiers. Since they are SS, they don't need filament voltage, real tubes do. So, you have to connect the 5Y3GT filaments to a 2A, 5V supply.

Here is the tube data for a 5Y3GT...

http://www.r-type.org/pdfs/5y3gt.pdf

It's really basic, a 5Y3GT is nothing more than two diodes tied together at one end...two plates (anodes), one shared cathode. But tubes need heat to work. This cathode is DIRECTLY heated, meaning that the filament voltage is applied directly to the cathode.

The red AC High Tension (HT) wires connect to the plates...Pin 4 and 6.

The DC B+ voltage comes off the cathode...Pin 8 (there are reasons we use Pin 8 and not Pin 2). This runs to your Standby switch if you are using one and then on to the filter caps and is distributed throughout the amp.

But this cathode needs to be heated to work...so we also connect the yellow AC 5V filament supply to Pins 2 and Pin 8 to heat that cathode and make it work.

I don't want to link to reference Fender's original schematic because we do things differently now...Fender used a polarity switch and unbalance filament wiring in the '50's, not something anyone would want to do these days. But there are schematics and layouts available through a Google image search from Fender, Mission Amps, Trinity, Weber, Triode, Ceriatone (Don't use Pin 2 for the B+!) and others. Compare and contrast.

[Tom Phillips]

...The output tubes (6V6GT) appear that the glass is blacked out, not clear, would this be normal for these tubes, just looks strange...

Yes. It may look strange but it was common in many original 6V6s. Apparently some manufacturer(s) are still making them that way. I would say that it's nothing to worry about.
Cheers,
Tom

[jim1976]

The Chinese kits are really top quality dont worry about that! there just as good as anything else out there! Where did you get it? marble or ampmart?

You know most of the speakers you see today and pay top dollar for come from china $20 a piece. Have a look at Guitar speaker-BH Speakers they make celestion speakers and the weber speakers too... often the label is made in the country there meant to come from thats about it.

It does seem weird but the heater is like everyone has said on the dc side but its isolated with its own winding.

[Geobee]

Thanks for the help, much appreciated. Just looking at the circuit attached, wonder why they want me to use the 5 volt winding as the heater for the 5Y3GT, instead of the normal winding, but then, as I look at it, it needs to be isolated from the normal heaters, due to the strange set up of the tube. Also, I don't intend using the Chinese transformer, instead a US made one, so I trust it would have the 5 volt winding also, as it is for a Fender tweed amp. I purchased my kit from Ebay,

[jim1976]

See the 5 in the 5y3 that means 5v heater filament dont use the 6.3 on that!!!! The chinese transformers are fine dont worry about that, there rated to 120ma!!! there is no tone in a dc power supply an extra $200 wont make better dc.
I know most people say ohhhh its chinese but who makes all the parts in your computer you reading this on? and you tv?? the list goes on... spend the money on an output transformer thats where it counts, $30us from triode for a classic tone and its money well spent.

[jim1976]

I'd love to see a 350v chinese vs 350v usa ac tone comparison haha... you know the transformer outside your house is probably from china, and american transformer in your amp will not filter out that....

[Geobee]

Thanks Jim, will be sure to use the 5 volt heater on it. Just thought that the winding quality would be better on a US transformer, as I have found in the past that some cheaper wire is not so great in the long run, but next time will try the Chinese units. The kits can be purchased with or without the transformers. Regards. Geoff

[wyatt]

Thanks for the help, much appreciated. Just looking at the circuit attached, wonder why they want me to use the 5 volt winding as the heater for the 5Y3GT, instead of the normal winding, but then, as I look at it, it needs to be isolated from the normal heaters, due to the strange set up of the tube. Also, I don't intend using the Chinese transformer, instead a US made one, so I trust it would have the 5 volt winding also, as it is for a Fender tweed amp. I purchased my kit from Ebay,

As noted, 5Y3, 5U4 5AR5, etc. all require a 5-volt filament supply.

There are (were) 6.3-volt rectifiers as well (mostly 9-pin "miniature" tubes) and many budget companies used the same filament supply as the great of the amp, but that's not a great idea because of increased AC ripple and the heavy current draw. So, if you look at most of the better brands of guitar and hi-fi amp builders who used 6V rectifiers, you'll see they used PT's that had two 6.3V windings...one for the rectifier and one for everything else. But...that's a tangent....

Can't comment on the Chinese transformers supplied. There are lots of factors for quality...the laminate material, the winding, the gap, etc....that are usually subpar in cheaper transformers. It's not just a matter of having the right voltages. I'm know there are plenty of quality transformers coming from China, but I prefer to have a middle man like Vox, Weber, etc. to back what I'm getting and warranty it (regardless of country of origin).

[Geobee]

Thanks to all for the great help, would be easier if kit suppliers could include a schematic that actually applies to the purchased kit, and not assume that everyone knows every circuit mod that could be used. They wonder why they get negative feedback on Ebay. Very easy to damage expensive parts when misled. Regards. Geoff

[Tom Phillips]

...wonder why they want me to use the 5 volt winding as the heater for the 5Y3GT, instead of the normal winding, but then, as I look at it, it needs to be isolated from the normal heaters, due to the strange set up of the tube...

Well consider this...There is no strange setup of the tube. It's just something that you are unfamiliar with and don't understand yet. If you are going to build amps AND you want to do mods then you will want to learn more about vacuum tube electronics. There are several discussions on MEF about books recommendations. One example is at http://music-electronics-forum.com/t31848/ . You can search out others too.
Cheers,
Tom

[Enzo]

While I prefer to always have a schematic around for anything I work on, the purpose of a kit is the customer can buy it, assemble it per the instructions, and have a working amp. it is not made as a electronics course. If you assemble the part board like the layout and follow any step by steps, regardles of schematic, you should have a working amp. The average kit builder can;t read a schematic anyway. When I was a kid, our TV set had a schematic taped inside the rear panel. I don;t recall that helping my mom or dad when the TV went funny.

[jim1976]

Well you know its a 5e3... its not like there aren't a ton of schematics on the internet for them, I guess you could buy the same thing of another supplier and for an extra $200 you could get a step by step. Hmmmm Do you want a step by step? just give me $200!!! haha.
Its good for you to work to get it right though you'll learn more about it. Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection... find the 5e3 on there and work from that. Oh and heres a good step by step not totally complete but its really quite helpful Amp Kit Projekte - Onlineshop Startseite

The 5e3 is great in that there is a ton of stuff out there to help you put it together.

[Tom Phillips]

...The 5e3 is great in that there is a ton of stuff out there to help you put it together.

Good point. In fact, right here we have this sub-forum specifically dedicated to the 5E3 with over 500 threads and growing.

[tubeswell]

Your kit suppliers "borrowed" and altered the schematic from Weber Speakers and just blanked out the company info.

And it looks like a pretty bad copy of Weber's schematic at that