Few changes to help my Chub Clem to handle EL34s

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Few changes to help my Chub Clem to handle EL34s

Postby justinsweber » Wed Jan 25, 2012 1:33 am

I want to share some recent experiences... My friend helped me to add the jumper from Pin1 to Pin8 allowing use of EL34s.
He remarked that the filaments appeared soft and we measured them. 5.8vac, and he thought the EL34s were drawing too much current. 6l6 are good for 1amp per tube plus 600mv for the 6SL7? So with 1 6.3 winding you're right at the edge? The EL34s use 1.5amps? Needing ~3.5amps?
Im using a XPWR105-120 which has 2 6.3 @ 2.5 amp windings. The current hookup only had me use 1... the yellow wires, with the brown 6.3 winding cap’d.
Using the EL34s, appeared to overrun the winding... too much current draw. So, we made sure the windings were in phase and combined them... Im not sure if this is paralleling or in series... The voltage did not go up, but it doubled the available current (amps).
2nd issues. The filaments still appeared (to his eye) to be dimmer than they should have been. So we measured the input voltage. With ~120v into the CL-90 the power transformer was only getting ~114v. Using a Varac @ 122v in, and the CL-90 still in place we had ~6.3. We placed a jumper across the CL-90... I know, thus killing its benefit, but allowing for a simple reversal. With 120v in and no CL-90, Im getting ~6.2 on the filaments.

Now the amps has the right amp of current available to the filaments to run either 6L6GCs or EL34.

Im a complete novice... but all this did seem to help make the wave form even soother.
Now for wattage....
The Tungsol 6L6GC Str RMS was 3.1 watts before mods @ 1000hz
The Tungsol 6L6GC Str RMS was 3.4 watts after mods @ 1000hz
The Wing’d C EL34s were 4.5 watts with mods @ 1000hz
All the wave forms were really clean, put till clipping.

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Last edited by justinsweber on Wed Jan 25, 2012 1:36 am, edited 1 time in total.
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Postby justinsweber » Wed Jan 25, 2012 1:36 am

Maybe the hook up diagram should paralle the two 6.3 windings as a default?
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Postby Shannon Parks » Wed Jan 25, 2012 5:54 am

Nice catch. Indeed, I've promoted using the PA774 (the Dynaco equivalent) with paralleled 6.3VAC taps in the ST35 amp for years, and for higher current tubes like the EL34, this is exactly what you should do. One issue with the Edcor taps is that filament taps don't mark the polarity, so I would just document the procedure for matching the taps:
1) If the VAC difference is around 0VAC, connect those taps together.
2) If the VAC difference is around 12.6VAC, swap pairs.
3) Always power down and give it a minute before reconnecting.

Don't worry about the filament voltage drop with the CL90, and please un-jumper it. It really tames startup voltages and will help the life of your amp.

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Postby justinsweber » Wed Jan 25, 2012 5:39 pm

Ill cut the jumper out... Its just the line voltage to the power transformer drops to 114v :-(.

We used the OScope to get polarity... Very easy.
Shannon, will you be updating your hookup sheet? Seems with 5amps avalaible could run even bigger tubes? (Like what tubes :-) ).

Thanx for all your efforts. Ive built or helped build 7 amps all with your PCBs inside.
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Postby Ty_Bower » Wed Jan 25, 2012 7:36 pm

separks wrote:Don't worry about the filament voltage drop with the CL90, and please un-jumper it. It really tames startup voltages and will help the life of your amp.


Or, if you feel better with the few extra tenths of volts, you could always put a 120VAC rated switch across the CL-90. Make sure you remember to open the switch before power on, then close the switch after everything has had a minute to warm up and stabilize.

The really clever will find a way to do the same with a latching relay and time delay circuit.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Re: Few changes to help my Chub Clem to handle EL34s

Postby Ty_Bower » Tue Jul 03, 2012 11:42 am

justinsweber wrote:Im using a XPWR105-120...


Oops. I hope you meant to say XPWR005-120.

The 105 is a 360VCT rated part, which really isn't suitable for this amp.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby justinsweber » Tue Jul 03, 2012 2:48 pm

Im using a XPWR005-120 which is what Shannon spec'd... was that wrong? now Im confused.
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Postby Ty_Bower » Tue Jul 03, 2012 4:42 pm

justinsweber wrote:... was that wrong? now Im confused.


Just a typo in your original post. NBD.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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