Paraglow - help! Its not a Paramour - sorry; Newbie -

[andrewuk]

That's certainly to be taken into account, thanks. Could I damage the C4S/sh-reg boards in this way? I have the Tucker upgrade circuit.

[Paul Birkeland]

What I would really like now (;-) is a brave discussion on improvements / mods!

I'd do your best to get the amps working in stock form first, then consider parts swapping.  Based on the collection of parts involved, I wouldn't want to add more variables to the equation.

-PB

[Doc B.]

One thing I recall about John's boards was that if you run the trimpot all the way to the end of it's travel before installing it you can blow the board. Be sure to use meter to measure across the pot (one end leg is connected to the middle leg on the PC board if I remember correctly, so measure from the middle leg to the leg that it does not connect to) before installing it and set it to approximately the middle of its range. I don't recall the value of the pot, but if it's a 100K, set it around 50K, if it's 250K set it to about 100K, etc. The idea is you want to make sure it isn't close to zero ohms.

[RPMac]

Andrew, have you gotten the information from Doc and John?

Paul, I think he is already past the "original" stock design that will corrolate to the original manual he will get from Doc. If he also has the original C4S boards (non-shunt regulated board) and the 5965, you are correct to build it stock by the manual first.

Doc, it is a 100K pot.

[Paul Joppa]

My thoughts on improvements are in my longer post, above. To my mind the most important is to get the operating points right, meaning you have to get it running first, then check voltages, and from there adjust the driver bias to get the right plate voltage, and then adjust the 2A3 cathode resistor to get the right current.

Direct coupling is a pain in the backside, no question. If it didn't sound good, nobody would do it!

[andrewuk]

Progress is slow - I'm back at work so other things must take up time.

I thought I'd knock up a couple of Camille CCS just incase things go wrong with the Tucker ParaglowMk2 and I can revert to Paraglowmk1. I've already found two very simple and fundamental probs with how the previous owner was wiring the amps up - almost too simple to see! That however is dealt with.

Back to the CCS...

Consider the Paraglow mk1's CCS (and also the Active SEXamp CCS in 'Valve' many moons ago.) I was soldering away merrily using 'verobard' and I thought, 'just a minute ...'
I have a few copies of another US magazine in which a contributor is using a Camille CCS and he reverses the pin outs of the two transistors (a 2N2097 equivalent (PNP) and MJE 350) such that the 350's emitter is down to the valve's anode and the 2907's collector is joined to the HT via a 100 Ohms current setting resistor. Surely this is a mistake! If Paraglow's CCS works then the other cannot!?

[andrewuk]

I've just found another on DiYAudio ... Again, the 2N2097's collector via the current setting resistor goes up to the HT of the circuit and the emitter of the 350 goes to the anode of the driver valve. The plot (for me) thickens! or in other words ... 'I don't understand!'

[Paul Birkeland]

It would probably help to post links to what you see.


For example, I found this image off of DIY audio that is consistent with our schematics:

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.diyaudio.com%2Fforums%2Fattachments%2Ftubes-valves%2F26720d1083627681-some-questions-about-c4s-ccs-adjustment-12b4a-active-loaded-linestage-small-.gif&hash=b98bc23c938371f9e94d78d7b1aa5c7d38c7e212)

In C4S construction, the collector always "feeds" the circuit...

There might just be something done differently in the drawing conventions that is causing the mixup.

[andrewuk]

Okay, I don't know how to do this but I'll try and take jpegs and post a picture. Though surely the paraglowmk1 or SEXamp C4s is well known and if you just picture that with the transistors reversed as I explained ... I'll see what I can do.

[andrewuk]

Aha! the posted schematic that I saw on DiYAudio gets corrected quite quickly but as far as I know the other example I came across is a very good (otherwise) looking example of a parafeed 46 SE amp in 'Sound Practices' in 1999 by a chap called Ross Lahlum. His is a great article and I built a couple of his CCS' and managed to lose them so I never got to fin dout how they sounded...ahemmmm (they are somewhere in this room!) last year. My experiments with 46s and then the 47s never got changed to anything unlike a 'Bugle' amp (i.e. 5751 as SRPP driving output triode, if I remember, My 47s are ancient globes - they look great!).

So, having sorted that out - onwards!

I'll look at the PSU now and see what I get with (and without) the shunt regulated power supply boards.

[RPMac]

Here are the voltages on my Paraglow II with Tucker shunt/reg boards and 6N1P.
All Magnequest iron
PGP 8.1 power tfx & RGC-6 chokes
EXO-03 plate choke & EXO-36 opt

2A3 cathode resister 3.3K

121.3VAC in
378VAC out

483VDC
471VDC after CLC

on 2A3
452VDC  plate
202VDC cathode
158VDC grid

on 6N1P
B1 158VDC plate
B3 2.45VDC cathode (332 R)
B6 224.5VDC plate
B8 5.8VDC

Only resistance out of tolerance were the B+ windings
140 & 149 where the book said 200.

PJ, do you see any adjustments I need to make?

Thanks, Robert

[Paul Joppa]

Wow - that is really sweet - unbelievably close to the ideal!

No adjustments. The 200 ohms spec is left over from the deYoung power transformer - you have the Magnequest PGP-8 so it's no surprise the resistance is different. Tuckers spec for B6 was 215 but I like your 225 better - keep it there.

Check the B1 voltage occasionally, once a year perhaps? It will increase as the driver tube ages. When it drifts to 175v the tube should be replaced. Controlling that voltage is the critical difficulty with direct coupling; it would be preferable to keep it in the range 145-175v. You are almost exactly at the center of that range, so no worries.

The high voltage exceeds the power supply capacitor rating of 450 volts. (This is another consequence of changing the power transformer.) I don't recall many problems with that, but the one or two in my dim recollection were on older amps. If this amp has seen a lot of hours, it might be prudent to replace them. Finding a cap with a higher voltage spec that also fits mechanically will be difficult, you may have to get the same 450v and hope the quality has not deteriorated. Difficult decision between preventive maintenance and "if it ain't broke, don't fix it!" ...

Hope that's helpful!

[RPMac]

Thanks Paul, but the credit for "ideal" has to go to the crew at Bottlehead...I can just solder and follow instructions.

Question on power supply caps. I have some CDE unl series 30uF 600V and 35uF 500V caps...can they work for the power supply? I already replaced the cathode bypass caps (had one to fail) with these. A single would be a tight fit, but if I need to parallel to increase the uF, that will be the problem with these amps. This question would be for my Parabee's also.

Those voltages were on my "good" amp that I got out of storage yesterday to make the measurements. The other amp will take a little more work, but I have some measurements before I put them in storage.

Amp #2

124VAC
388VAC out


486VDC
472VDC after CLC

on 2A3
448VDC plate
219VDC cathode
178VDC grid

on 6N1P
B1 178VDC plate
B3 2.44VDC cathode (332 R)
B6 227VDC plate
B8 6.97VDC

[Paul Joppa]

The UNL caps would be great if you can fit them in; I think since you have a 10-henry choke in the power supply that 30uF is enough. Google for the data sheet to see the voltage/lifetime tradeoff (very interesting) - figure at least 60 degrees C under the hood. I'd go for the 600v rating, especially on the first cap of the filter.

It looks like the B1 voltage is a little high. If the 6N1P is old, replace it and see if the voltage comes down; you want around 150v with a new tube. We've seen inconsistent service life with 6N1Ps; look for the older Svetlana 6N1P-EV if you can find them at a reasonable price.

You can trim the regulated voltage (B6) a little higher as an alternative, but if you go too far the B8 voltage goes high and destroys the reg chip - serious pain in the butt! B6 must be at least 50 volts greater than B1 to avoid premature clipping of the driver. Unfortunately I don't know the resistor values on the board so I can't estimate a reasonable value, but 250v will likely be OK.

[andrewuk]

Its odd, I am taking this very slow ... as I think the geezer wot I bought this off was doing. I am very busy at work and have several projects on the go - the icing on the cake is this one - but with a 27 / 47 tube pre here and ressurecting my 833s there; the GM70s have been in the shed for too long and those sweet el84PPs ... As my beloved has started redecorating after some serious house readjustments I don't get to play and listen and I'm in a bit of a mess. Sorting it all out is fun but frustrating. Of ate I hav been listening to my rebuilt ESS AMT1Ds with solid state amplification - Heresy!