• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Easy DIY tube amp

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#4
I can recommend the Tubelab Simple PP. Have built some amps, a couple of el84 pp, but I did not like the sound I got from them! But then I found the schematic of the Tubelab el 84 PP, built the amp, , and the amp sounded just fantastic. Built point to point soldering.
 
#9
#11
The general consensus is that toroidal OPTs are less tolerant of DC imbalance than standard EI OPTs. I made a clever little mod to my Tubelab SPP (stole the idea from the no longer available DIY Tube EL84) where trim pots are wired into the cathode circuit of each EL84. This enables perfect DC balance between pairs of tubes. It also allows rebalancing as tubes age.

If you are thinking of building one of these you should probably buy tubes sooner rather than later, the current geopolitical situation being what it is. The Tubelab SPP uses four EL84, two ECC81 and one GZ34. The GZ34 may be replaced with SS diodes but it would be best to change the power transformer to one with a 275-0-275 volt secondary when using solid state rectification. The GZ34 version typically uses a 300-0-300 secondary.

Good luck,

Steve
 
#14
Found it thanks
SimplePPschem3.GIF
 
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#15
I've changed this circuit a bit, see attached. I replaced R1 with a choke to kill the last bit of PS noise. Doing so made this a very quiet amp. So quiet it could be used with high efficiency speakers.

I changed the value of R3. 10K is from a later version of the parts list.

S.
 

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#16
Hi Steve,

Thanks for the updates.
For the orange diodes: 1N4008?
What is the value of the C101 capacitor in parallel with 5K1 (in the feedback loop?)

The project has officially started: SPP board and OPTs ordered.
Found local suppliers for all tubes, russian-made 😱
I have some trouble locating a suitable 230V power transformer: from what I read secondaries should be something like this: 300-0-300@200mA, 6.3V@5A, 5V@3A ?
Cheers,

Jacques
 
#17
Steve,

Many thanks for your SPP schematic post. I am currently building an EL86 version of the Tubelabs SPP, and working with the “blank schematic”, as in post #14, is a pain - I did not know you had added the part designations. Thank you!

If I may digress for a moment, I’m modifying my build to use ~270 V as B+ for the EL86 plates, regulated screen voltage of ~200V and fixed bias (via Gillespie’s EFB circuit), and 320 V on the front 12at7 plate supply. Experience of other builders showed that the “standard EL86 SPP implementation” results in too low a supply voltage for the driver/splitter to drive the EL86 with higher drive requirements than a EL84.

I wish we could compare my EL86 version with your EL84 SPP. And your Jacques! Good luck with you build.
 
#18
I use HER108 diodes, they are less noisy than the 1N400- series. 1N4007 or 8 should work fine though.


Have a look at this P. T. from primary windings, the 6.3v 2A winding is tapped at 5 volts so this would work for the GZ34. The GZ34 only needs 1.9 amps for its filament. https://primarywindings.com/product/mains-transformer-mullard-5-10-stereo/

C101 will depend on the output transformer. A square wave generator and a 'scope is needed to determine which value is best. I haven't used this out yet on my Hammond-equipped SPP . Guess I should stop being lazy and just do it.

S.
 
#19
jacques antoine said:
I have some trouble locating a suitable 230V power transformer: from what I read secondaries should be something like this: 300-0-300@200mA, 6.3V@5A, 5V@3A ?
Click to expand...
Jacques, That is what Tubelab tells you, but in my experience that gives you B+ a bit on the high side. Yes, you could always make that transformer work (by fiddling with smaller input cap, and/or series resistors).

Steve, did you use a 300-0-300 transformer?
 
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#20
Jacques:
See attached bias mod. If you'll be using Toroidal OPTs you might want to implement this for DC balance. Four needed, one for each EL84. Measure voltage across the 10 ohm resistor and set trim pot for desired current flow. I typically use 0.35 volts which = 35mA.

S.
 

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