New member, first amp build!

[DarDar]

Hello folks!
OK Let's see I bought a Martin Acoustic last Christmas and started learning chords, and said to myself geez I'm gonna also need an electric, so I bought a kit and built my first electric, an SSH Strat clone and now I'm working on building a Fender Deluxe 5E3 amp clone. I'm waiting on just 2 parts to come in this week and I'll start soldering the board to the chassis. Progress pics are below. I'm doing this totally scratch from the schematics (no purchased kit) so I don't have any real instructions and need to know where to go once I've got everything completed and tripled checked all my work. I've tinkered with electronics but have never fooled with tubes other than using tube testers in the five and dime stores about 35+ years ago! (Yes.. I'm an old fart)

Hopefully those who read these are the type who believe that there's no such thing as a stupid question! )

A few questions for now include:
1> Do I need a Variac for slow startup(smoke test), and burn in? I have a 15 volt AC source, would that be ok for startup or do y'all just let her rip???

2> I've seen an article on using a 1meg resistor to ground to check current flow across the resistor. Is this a recommended method? If so which points do I check and do you keep these permently installed? Is there a table/guide for recommended values?

3> I'm assuming rectifier tubes don't need adjustments. Do you need to check if the rectifier produces waves of the same amplitude for each wave half to check for a good rectifier tube?

4> I hear about biasing but none of the schematics for the 5E3 show where a trim pot would go. Does this amp build not require any biasing?

5> Will an oscilliscope be necessary for checking waveforms or will just checking test point voltages with a multimeter suffice? What are the normal tolerances for the test point voltages? 5%, 10%, 15% ???

6> Does anyone have a link to any good articles on starting and setting up a new amp?

The 5E3 deluxe schematics I'm working from are the version which has 3 fuses instead of one, and an extra X type Safety capactor. I added a few turrets to relocate a couple of resistors. and install the X2-cap (not shown in pics)

Sorry for the long note. I'm hoping that if y'all don't have the answers that y'all can point me to some documentation. I've been doing a lot of googling for documentation and came across this forum! Any help is fully appreciated!!

Thanks, Dar


Chassis back with sockets mounted
Mainboard
Power and Output transformers installed front view
1 x 5Y3GT(rectifier), 2 x 6V6S(power), 2 x 12AX7(pre-amp)
Overview...

[tubeswell]

I'm doing this totally scratch from the schematics (no purchased kit)

Best way to do it.

1> Do I need a Variac for slow startup(smoke test), and burn in? I have a 15 volt AC source, would that be ok for startup or do y'all just let her rip???

Nah - 1stly with the tubes out, just make sure you've got the right amount of VAC across the respective PT secondaries.

Then switch it off and plug your rectifier only in, and make sure you've got a ballpark DC B+ voltage on your first filter cap node

Then (switch off again and) plug your other tubes in and check the plate, screen and cathode DC voltages at idle (i.e. without an input signal - vol cut) and report back.

Be ultra careful measuring the voltages - don't kill yourself

2> I've seen an article on using a 1meg resistor to ground to check current flow across the resistor. Is this a recommended method? If so which points do I check and do you keep these permently installed? Is there a table/guide for recommended values?

Not necessary - just check the DC voltages at idle as per above

3> I'm assuming rectifier tubes don't need adjustments. Do you need to check if the rectifier produces waves of the same amplitude for each wave half to check for a good rectifier tube?

You'll almost never get perfectly balanced rectifier anode voltages. Don't worry about it. As long as the rectifier produces around 340-370 VDC (or thereabouts) B+ at idle, with all the other tubes plugged in, there's no need to panic.

4> I hear about biasing but none of the schematics for the 5E3 show where a trim pot would go. Does this amp build not require any biasing?

The traditional 5E3 is a cathode-biased amp by design. There is typically a 250R - 270R resistor to ground (that is bypassed by a 25uF 63V-100V cap - in parallel with the resistor) that is shared between both cathodes of the 6V6s. That is the resistor that sets the bias by putting the cathode at a +ve voltage with respect to the grid(s). Assuming your amp is a 'typical' 5E3, then once you have the amp up and running, there should be no further bias adjustment required for 6V6s. (Fixed-Bias amps on the other hand - which supply a -ve voltage to the power tube grids, are a different story, and are more finickity - but you don't need to concern yourself with that)

5> Will an oscilliscope be necessary for checking waveforms or will just checking test point voltages with a multimeter suffice? What are the normal tolerances for the test point voltages? 5%, 10%, 15% ???

Handy but not really necessary. If you have one handy then by all means use it to satisfy your curiosity. But if the amp is working properly without any weird noises, its superfluous. Even if it does have weird noises, most things can be worked out without having to resort to a scope.

6> Does anyone have a link to any good articles on starting and setting up a new amp?

Read the Jack Darr book (for basic intro to guitar amps) here:

Jack Darr Book, chapters 1 - 8

The 5E3 deluxe schematics I'm working from are the version which has 3 fuses instead of one, and an extra X type Safety capactor. I added a few turrets to relocate a couple of resistors. and install the X2-cap (not shown in pics)

Can you post a copy of the schematic you are using?

[loudthud]

The extra fuses are for current safety standards. The theory is that if a short occurs on any transformer winding that the main line fuse might not blow resulting in a fire. You can include them if you want. Many people leave them out.

The X type cap: If is goes from one side of the power line to the chassis, that's the so called 'Death Cap'. It's not needed if you have a 3 wire power cord and it's a safety hazzard, leave it out. If the cap goes across the power line or a transformer winding, it's for noise filtering. Probably not needed but shouldn't hurt to include it.

Normally, voltage readings are said to be +/- 20%. They depend mostly on exactly what transformers you are using, the line voltage and tubes. Most of the time if you are 'in the ballpark', you are ok until you get down to the nit picky stuff. If you build another amp with the same parts, the two amps might be within 10%.

[mbailey]

WELCOME
I am relatively new here but you have come to a great place I have always got great friendly responses when ever I've asked a question and have never seen anyone treated bad for asking a question even if it might be considered dumb by some of the more experienced guys. the most important thing is be safe

[grod915]

6> Does anyone have a link to any good articles on starting and setting up a new amp?

I like this site for startup:
Paul Ruby Amplifiers

[DarDar]

I just wanted to say thanks for all of the information links as they are very usefull. The schematics I'm using are from here...

http://www.fender.com/support/amp_sc...0JUN%2007).pdf

Which are similar to many 5E3 schematics I've seen but with the X2 safety cap, the NTC10 thermistor and two extra fuses. I will have a 3 wire power cord with ground so the X2 cap is mainly for noise suppression. The Thermistor is for initial 'power on' surge supression and the two fuses is to protect in case of PT shorts/failures. I assume I could cut out all of these for ease of building but I don't mind the extra safety if it's worth it. I'm trying to decide on whether to put grounds as shown in the last page of the schematics pdf file, or use a star ground or solder a buswire across the back of the pots and attach all grounds there. Any preferences from you guys due to experience?

Anyway thanks again for your time as it is appreciated very much! I just have to get over this flu so I can get back to work on this project as I'm getting anxious. Thanks for the safety tips. I hope to retire in a few years and don't want to zap myself after working 35+ years to get there! Plus I'm not going to let my wife get off that easy! It's her turn to have to listen to some screeching noises for a while! Paybacks hell! )

Thanks again,
Darwin

[loudthud]

Thanks for the link to that schematic. It's pretty true to the original but has all the updates that are usually suggested and the safety updates. BTW your build looks really good. Nice work on the chassis and eyelet board.

In one of your original questions I think you meant 1 ohm, not 1meg. In a cathode biased amp like the 5E3, they usually arent included. They allow you to measure the current through each 6V6 which is one of the things you need to know when evaluating the output tube bias and balance. The so called 'bias probe' does the same thing. You can get a fair idea of the bias point by just looking at the voltage across the 250 ohm resistor and the B+ voltage, but you can't tell if your tubes are matched.

[DarDar]

YEEEHAAAAW!
IT WORKS!

No burning smells, no smoke, no fire! And most importantly, no electrocution!

MANY THANKS to the folks who gave me advice. Especially on the link to the initial power up sequence testing.

It took me a while to locate two parts. The X2 Type Safety Capacitor I had to order from a mom and pop shop in Canada. The thermistor was a pain to find as well. Seems like there are tons of places to buy some of these in the US... that is if you want 4,000 of them! I modified the wiring layout a bit since I didn't find a board like the one in the drawings, (plus I was short on space). It got real tight in places and I had to stand on my head for some of the soldering. That's why a few of the solder points could look a little better. Plus I'm about half blind! I had to wear some +3.5 readers over my regular scrips for some of the work. I hooked it up to an old speaker so I'm not sure what the finished product will sound like yet until I get the Jensen in a cabinet. Sounds ok so far!

Anyway.... I'm just happy I got it all right and encountered no problems on the first power up sequence!

Here's a few pics...

Front
Back
Power and Rectifier tube
Full view


Next up is the cabinet. I have all of the tweed cloth, grill cloth, handles, feet, speaker, etc.. I have all wood for the front and back panels but I need to go buy some wood for top, bottom and sides! Gonna have to pull out the table saw (buried in the storeroom with a mountain of crap on it) and pop the dado blade on for making 'fingers', which I've never done before either. Hopefully I'll have pics of the full build soon.

Well I built my first guitar the first of this year and hope to finish my first amplifier build in a few weeks (Vacation coming up). Who says you can't teach an old dog new tricks?? Now if I could just learn to play!!

THANKS AGAIN!
Dardar