Budget 5E3 Head

[haasamps]

I had a Weber Reverb unit PT sitting on the shelf that puts out enough juice to handle a pair of 6V6's (260V@100mA, 6.3V@3A), so I thought it would be to build a 5E3 "inspired" head in a very small package. I've built two 5E3's in the past, both of which have found their way to new owners, and I missed having one around.

Some may take offense at me calling this a 5E3, since there is no 5Y3, and plenty of other changes from the original.
Those changes include:

• SS Rectifier
• .02 Coupling Caps in the preamp
• .05 Coupling Caps from the PI
• 1M Grid Stopper to the Cathodyne
• 22K Grid Stopper to triode before the Cathodyne
• 470R Screen Resistors
• Second dropping resistor in the power supply dropped from 22K to 10K to account for lower B+
• Single input jack with toggles to select Bright/Normal/Bridged input.

As mentioned I used a Weber WRVBPT PT and for the OT I used a Magnetic Components Stock 5E3 replacement, 8K/8Ω

With this setup I got a B+ of 340 and 328 on the 6V6 plates.

The amp turned out great, IMO, better than I expected really. I was a little worried about noise, due to the small chassis, but a little re-routing of the PT secondary leads took care of some hum on initial power up. Now the noise floor is very low. I played it at a bar gig last weekend through a 1x12 open back cab with an Eminence Cannabis Rex in it. We played 45 classic rock covers from clean to mean with nothing but a clean boost on the floor, which I only used a handful of times. It's nice to have a 5E3 again!

[Steve Conner]

Very nice!

I have no problem with SS rectifiers. I use them in all my builds: it's one less tube to wear out. But the purple velvet covering...

[haasamps]

Very nice!

I have no problem with SS rectifiers. I use them in all my builds: it's one less tube to wear out. But the purple velvet covering...

Hey Man, chicks dig the purple velvet...at least a couple at the gig did. "Can I touch it?"

[Chuck H]

This guy's gonna fit right in.

[barfoden]

Great little amp..

Nice to see that the 5e3 can be made cheap and still sound good.
Do not worry much about the lower plate voltage... I think Bruce collins say that a pair of 6V6GT will make a decent amount of output with plate voltage above 320V. As long as the rest of the parts are designed right.
A guy measured 11 watts from a 5e3 build with a GZ34 rectifier, small PT with 250V@75mA and a +B of 324V.

I got a nice 15-20 watt 8K OT from ampmaker.com and Barry at ampmaker has a PT of 275V@100mA,6.3V@3A, 220-230-240V primaries. By using your voltage readings, this PT with diodes will give me ~360V +B and ~ 345-350V plate. Perfect for a 5e3 with a 270 ohm bias resistor.

Another powerfull "5e3" amp is the DeArmond R15. It has large transfomers but with lower plate voltage of 330-335V (original values), and a 2.7K dropping resistor, more main filtering (40µf with a 5y3 which does not sound right as the limit should be 30µf with a 5y3) and a 250 ohm bias reistor. It is said to be a less compressed and more powerful than a 5e3, and it uses 0.047µf coupling caps in both preamp and power stage.

I see that you added 470 ohm screen resistors. Is that really needed with the 4.7K screen dropping resistor and low plate voltage. Some people says that it has a slight negative effect on sound. I think it is nice to have screen resistors in there so you can measure screen current but would use a little lower value (220 ohm) if there is a large screen dropping resistor (4.7k) in the amp. The 470 ohm screen resistors in a deluxe reverb is a different matter as the screen is choke fed with 150 ohm of resistance and the plate are connected to a ~ 150-200 ohm OT resistance which sets the screen voltage higher than plate.

With the 5k screen in the original 5e3 the voltage will decrease a bit when the screen and preamp are sourcing more current. This gives the 5e3 a lot of compression and less headroom. Especially with the 16µf plate filter cap in the original amp.

My high headroom cathode biased Laney (4xEL84) amp (32 watt) has very little resistance between the plate and screen (470 ohm) but has 2x50µf main filtering to decrease DC ripple as the small screen dropping resistor does not filter much ripple.

You also decreased the preamp couplers to 0.022µf and power couplers to 0.047µf. Is the amp still "fat" sounding ??. The power couplers are still plentiful at 0.047µf but I read that with the special layout of the 5e3 preamp with no 270k resistors to decouple the two channels, the coupling caps need to be large as you would loose to much bass when you are turning down the volume.