if one could?

[Thoburn]

The Paramour was never a problem for the EML tubes and neither will the Stereomour be a problem. They are both capacitor coupled between the driver tube and the 2A3, and thus the EML tube is protected at startup.

I'm not going to ask for you to guarantee it, but from your statement I will keep the EML "Mesh Plate 2A3" on my 'wish list'. I is rather pricey though.

[Doc B.]

The Paramour was never a problem for the EML tubes and neither will the Stereomour be a problem. They are both capacitor coupled between the driver tube and the 2A3, and thus the EML tube is protected at startup.

Hi Doc,

What do you make of the EML ban on paper and oil coupling capacitors? (I have Jupiters for instance, which are beeswax and paper (oil??) )

On the EML site I think I ban on 'Large' coupling capacitors as well.

I don't know that what I think is relevant to what EML's policies are about capacitors. Clearly the pages of boilerplate on the EML site indicate that there are a lot of parts and circuits out there that the EML management feels are incompatible with their product. If something bad happens the tube guy is maybe gonna say it's the amp maker's fault. The amp maker is maybe gonna say it's the tube maker's fault. Whatever. The bottom line is the all the amp maker needs to do is supply someone else's tube that works in his amp in order to play it safe. The tube maker either has to come up with a solution or generate a list of warranty violations. I'd rather be the amp maker than the tube maker in that situation.

Once again, I think the EML tubes can sound very, very nice. For ten years the only tubes that arc over on startup in our DC amps have been the AVVT and EML tubes. It appears by now that this tube maker is not going to make changes to try to achieve the same level of compatibility with our direct coupled amps that other tube makers already have. So we simply sell a bunch of 2A3 amps with someone else's tubes. Even though we can just continue to do that and say "using EML tubes in our amps will violate your warranty with EML (note here that the warranty on our amp is not voided, but we will not replace your EML tubes if they go poof)" we have come up with a circuit that should make the EML 2A3 usable in our amp - assuming that the research that the manufacturer sent us and the conclusions he has drawn are correct. I don't have any problem with doing that, and I want to try to help our customers who are otherwise caught in a standoff.   

My experience in the industry is that we have the greatest success when we work with suppliers who are equally willing to adjust and adapt their product to work with ours as we are with theirs. A great example of this would be Mike LaFevre of MagneQuest.

[Paul Joppa]

The problem seems to occur when there is a positive grid voltage an/or grid current during the warm-up of the filament in EML tubes. Even a tiny leakage current in the coupling cap can create a hefty grid voltage before the filament gets hot enough to allow grid current, which I assume is why they ban any cap that can have significant leakage. Also, large-value coupling caps in combination with high grid to ground resistance makes a long time constant, and the charging current of the coupling cap can cause this high grid voltage for enough time to occur during the filament heating. I don't think there is a problem with 0.1uF and 250K ohms, which is what we usually use - but some amps use 0.47uF or even greater coupling caps.

In my humble opinion, EML is taking their best practical line here. Their tubes sound really good, and there is a high probability that is partly because of the cathode they use. So changing their tube's design would risk damaging the sonics, and the tube works well with many - probably most - amplifiers. They are up front about not using the tube in amps that can damage it.

You could say the the esoteric tubes are find in normal amps, and normal tubes are fin in esoteric amps, and of course normal tubes are fine in normal amps. It's the combination of esoteric tubes in esoteric amps where unexpected problems sometimes develop.

[howardnair]

if one could?-- i would!! and did-sooooo!! i ordered the sophia princess 300B 2.5--why?  well pure and unadulterated curiosity--whether i chose the sophia 300B 2.5 or the princess 2a3 -a pair of rca blackplates-or even the emission labs--what i will have is music!--i worried about caps and resistors , speaker terminals ,goldpoint selector or stock -alps  or stock-wiring layout-and on and on--before i built --then the wooden chassis-[i had to make quite a few prototype pieces]-the finish on the chassis-then consternation about upgrading the tubes--yikes--i would not have done it any other way--very enjoyable--so i will put the sophia's in the stereomour--and sit back and enjoy-i still say that the stereomour is more than  a improvement over my cayin 860 modded mono blocks which are still resigned to the basement system and most likely will stay there until i sell them and build another something or other--howie

[Thoburn]

if one could?-- i would!! and did-sooooo!! i ordered the sophia princess 300B 2.5

Hello Howard,
Did your tubes arrive yet? Any first impressions you care to share? Inquiring minds want to know.

[howardnair]

thoburn-Ye of Inquiring minds--i am very pleased with the sophia's-the sound in general is much more filled out-the bass especially-nothing is missing in the midrange and highs----{not that the shuaguang 2a3-c is a bad choice]---i hear more of the nuance of the music and the soundstage is very good-this with jazz- miles davis, kind of blue --glenn gould, bach --joni mitchell ,hejira-all lps--fm radio classical/rock--and my reel to reel, dave brubeck-i will put some rock on this evening-all in all good right out of the box-
a hhh yes  HAPPY THANKGIVING EVERYONE--HOWIE

[Thoburn]

Hi Doc,
What do you make of the EML ban on paper and oil coupling capacitors? (I have Jupiters for instance, which are beeswax and paper (oil??) )
On the EML site I think I ban on 'Large' coupling capacitors as well.

I don't know that what I think is relevant to what EML's policies are about capacitors.

What I am really asking is, "Would my Jupiter caps be a problem for the EML tubes"? They are not exactly PIO, but then I am not well versed in capacitor factors.

BTW, We live in Gig Harbor and are snowed in as well. May not be able to make it to my sister's house for turkey. Really sorry I sold my 4x4 pickup.

[Doc B.]

Safe bet is don't use them. One the one hand I have a pair of custom Jupiters they made for me about 7 years ago that have held up beautifully and sound great in a big custom preamp with plenty of air flow and a very conservative voltage relative to the cap rating. On the other hand we have seen several Jupiters fail used in a S.E.X. amp chassis where it gets very warm. The Stereomour should run a bit more cool under the hood because of its vents (and the Paramount is pretty hot underneath - no Jupiters!), but I wouldn't take the chance. If you do decide to use them, keep them away from the hot bits.

No sign of the rain that is supposed to melt off the snow today. Looks like we may miss our big family Thanksgiving too.

[pboser]

The EML tube cannot handle the startup cycle of the present, no soft start ParaMOUNT 2A3 amp (or the now retired Afterglow/Paraglow), which is direct coupled between stages.

Doc,
I'm using my verable Afterglows modified to use 45s.  Is there a soft-start mod I could do to preserve the output tubes?  Some ideas I've had are to put a damper diode in the PS (but where would I put the tube??), or one of those delays I've seen somewhere to slow down the B+?  Of should I leave well enough alone?
Thanks,
Pete

[Doc B.]

Are they arcing at startup?

[pboser]

No, they're just elderly, and I was considering steps to increase their life.................

[Doc B.]

I think with this, what, Mk IV version of the SRC4S board? we may get a manual written for its general use in other circuits, and of course this one allows for the implementation of a form of slow start that addresses the direct coupling of driver and output tube.

The versatility of the SRC4S makes writing a manual for it a real challenge. What we can do is give folks the basics of how the thing works and how to generally calculate the component values on the board. But the sticky part becomes whether or not the builder has knowledge enough to derive what voltages and currents they may need for a given circuit, and what changes they might need to make to the power supply.

Certainly to some extent we can help folks here, particularly with something like our legacy kits where the operating voltages and currents are known. What we haven't worked out yet is how to support the use of the board in modified or non-Bottlehead designs.

Give us a little more time to get this kit out as a Paramount upgrade first, and then we will look into writing some instructions for more general applications.

[pboser]

OK, I'll keep an eye peeled for more general applications.  Thanks!
Pete

[Paul Joppa]

...
I'm using my verable Afterglows modified to use 45s.  Is there a soft-start mod I could do to preserve the output tubes?  ...

How old, exactly, are these amps?

The early Afterglows derived the driver plate current from the output tube cathode, and could not drive the grid positive under any circumstances. This appears to be the main danger to the new EML tubes. Not having tried it, I'm not going to guarantee it will work safely, but if it doesn't I'd be quite surprised.

This design makes it impossible to shunt-regulate the driver power, which is part of the reason the later designs (including the 2A3 Paramount) do it differently, but if you're cool with keeping the old design it does have that virtue.

As for extending the life, the power supply capacitors were electrolytics operating close to their maximum voltage specification, so replacing them might be a good idea if they're more than a decade old.  The actual voltage depends on which power transformer you have (there were several) and of course on your line voltage. If you post the tube pin voltages, we can assess that situation along with the operating points which may have drifted - the bane of direct coupled amps.

[pboser]

Thanks for the reply, Paul.  I can't pinpoint when I built them - I had a pair of the original SEX amps, then got the TFA-204s to upgrade them, then got the Afterglow kits to use the '204s.  I wasn't aware of variations on the Afterglows, but I'm certainly open to modifying them. The only mod I've done since I built them is to change the cathode resistor to use the 45 output tubes.  I won't get to check voltages today, but I'll take a look soon.  Is there a schematic of the later/latest version available?
Thanks again,
Pete