Paraglow (2005) instructions and schematics needed..

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Bluesman

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Hi guys - first post. I´m Rick, from Sweden and a seasoned tube amp builder. Mostly, I do guitar amps - restaurations of vintage stuff and I also builds replicas of old low-power amps.

This time, however, I have my hands on two Paraglow kits, bought back in 2005 and never assembled. Of course, my friend the owner lost the instructions for assembly and most important - the scematic way back. I need both, since I am finally building them now.

If the kits are from 2005, I assume there are revisions or upgrades. But for now, I´d like to see the original paperwork for the straight kits as they were sold.

If necessary to define a circuit revision, I have the checked packing list here with the part numbers where necessary.
Dated and signed 19 Sep 2005 :-) by Doc B(?)

Any tips and pointers?
TIA /Rick



 
The Paraglow kit is closer to more like 1995. 

PJ and Doc B. will remember the specifics better, but I think you may need to take a rough inventory of the parts and let us know exactly what you have.  There are certainly some changes that should be made to the original design, mostly having to do with the wattage of the cathode resistor, but that can all be sorted out once it's certain which kit you have.

You may also find it much, much easier to pluck some of the tastier iron tidbits out of the Paraglow and build them into a Paramount, as the Paramount will give you a fused IEC entry, more room to work, and all the updates you would want anyway, with advances like DC heaters with filament chokes, a shunt regulated driver stage, and high quality teflon coated wire.  (The wire supplied with the original Paraglows is nice sounding stuff, but tough to work with) 

-PB
 
I can send a link to a copy of the manual. Contact me by PM with your email address. Also it would be helpful to have the name of the original buyer if you have it.
 
Thanks for the advice so far. I´ve made a crude scan of the packing list.
For now, I will just implement a proper wall connector type (IEC?) and make proper fusing arrangements for the power tranny primary & secondary.
I´d like to get this beast up and working before any upgrades, unless they are really important/safety related or really simple.

Let´s see how this attachment thing works out.
 

Attachments

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Dang, that was LIGHTNING-FAST service if I ever saw such a thing :-)

The original buyer is Anders Nilsson, Malmö, Sweden, your sale date 13 June 2005, sale no 5646 :-)

But: the forum says  "DocB has blocked your personal message" when I try to PM you.



And thanks a million in advance for the help!

Cheers /Rick
 
My goodness, we better not let Josh see how short that list is!

The 3K 12W resistor is run well under 12W, but it still gets way to freaking hot for its own good.  When I get Paraglows in for repair, I use four 3K 12W resistors in series/parallel to get a 3K 48W resistor (which runs cooler and may outlast me!). 

At bare minimum, I would suggest replacing that part with a 3K 20W resistor.  If available, a 3K 25W part would be what I suspect PJ would recommend.  I also ended up mounting this part between the two 5 lug strips which end up holding some power supply parts and the cathode bypass cap, but your mileage may vary there.

-PB
 
Ok, I´ll have a look in my stash of power resistors to see if I can fix that issue. Good point. Thanks. I may have ceramic hi-wattage resistors of that order. Wirewound or ceramic wouldn´t make much difference if they´re close in value, right? Don´t tell me they sound different :-)
And teflon wire (multiple colors, single strand, good isolation specs) I do have.

/R
 
There's a big old cap sitting across that resistor, which generally helps mitigate the sonic contribution of the resistor, but at the same time makes capacitor selection pretty important. 

-PB
 
Ah well...the cathode cap has stuff to do dealing with the frequency response and gain of the output stage, agreed. Until I´ve seen a scematic I can´t say more.

One thing strikes me as odd: there seem to be a couple of carbon comp resistors in the kit...why on earth? Mojo?  8) I tend to stay clear of these anywhere near the signal chain, the noisy b*stards. I might be wrong about them being carbon comp, tho.

Edit: i was wrong. Carbon FILM it is.
 
Carbon comps do have their uses, though we are phasing them out due to physical durability more than anything.

The carbon film resistors in the Paraglow are generally for biasing the LED string on the C4S board and bleeding out the power supply capacitors, and neither role has ever stricken us as being particularly important sonically. 

-PB
 
Please allow me to differ, but carbon comps are way past their prime/best before date in any modern design. Flame-prone, mechanically loony, value-drifting noisy buggers. I have repaired too many AC30 amps from Vox, probably. Now...where was I?

Edit: yes, in your applications, I am sure they work - no criticism there. It´s just me being allergic :-)

 
They are indeed mechanically loony, but if you have an application where you want something that stays resistive at obnoxiously high frequencies and isn't dissipating any power, they work pretty nicely.

It's funny, if you read about them online, you'll see articles that cal them "inexpensive" and "high reliability", which seems overly generous/outdated on both accounts, but somehow I still run into them in new production electronics from major manufacturers from time to time.  (The last time in a commercial thermostat that's no more than 10-years-old. 

-PB
 
True. But as most of them are/were installed in vibrating cabinets with lots of heat present, as in a guitar combo....I´ve seen so many CC resistors with hairline cracks = intermittent opens, drifted beyond belief and...just acting as bad, cheap and unreliable fuses. CC screen resistors in a 50 W amp that have taken out tubes, sockets, output trannies when failing... = allergic :-) And...If I ever build a HF/VHF/UHF/SHF PA again...those CC:s wont even get close to me, no matter what mojo brand they are..  Ah well. OffTopic. Didn´t want to raise a point, just trying to get this amp to work :-)
 
The biggest issue after the under-rated cathode resistor is that the PGP8.x power transformer generates significantly higher voltages than the deYoung, around which the amp was originally designed. If your power transformer has solder terminals and no lead wires, then it's a PGP8, the 230v version was called PGP8.2.

No reason not to build it as designed at first, but once it's running please post again and report the voltages (from the tests at the end of the manual). Given those I can advise changes to optimize the operating point and enhance reliability.

The operating point is always difficult with direct coupled amplifiers, and it is easy to get it badly matched to the output transformer impedance, and/or operating the 2A3 beyond its capabilities. If you've worked on AC-30s, you know about running power tubes above their rated dissipation! In our current designs we use trimmers or servo bias schemes to establish the operating point reliably; experience with the Afterglow and Paraglow is the reason we have adopted these strategies.

When running right, this was our best sounding amp for many years and I have a great fondness for the circuit even though it's not my design. Credit John Tucker and Doc B for the design.
 
Good point. Thanks. I have the 230V tranny with solder lugs, and I need to know the windings / details before I apply any tricks from my book. Maybe there´s a 240 or even 260V primary tap I can use without upsetting the filament voltage too much. Most power tubes that I am used to can take a good beating if you regulate their screens with a couple of Zeners that bring the screen voltage down to a healthy level, but these...ah well, we´ll see. Thanks again for the heads-up!
 
I'm happy to help and send a copy of the manual for this long retired kit, however I would suggest that it's not very logical to challenge design choices and at the same time ask for help understanding how the circuit is laid out. There are updates that are more important than worrying about the carbon comp grid stoppers.  As long as you don't ham fist the stoppers when installing them they will work fine.

To make the amp as reliable as possible uprate the wattage of the cathode resistor as suggested and also use higher rated caps in the power supply, as the B+ can exceed the cap voltage rating in some situations and typically runs close enough to the limit that we have found those caps can fail after about ten years. We typically use two 270uF 350V rated caps in series with appropriate compensation resistors when we retrofit the original 100uF 450V caps in Paraglow and Parabee.



 
Doc, please don´t see it as a design challenge. I was just stumped there for a while, coming from a different world. No offense, please.

I´ll have a look at what caps and cathode resistors I have in stock here and take appropriate action.

Cheers /Richard
 
Well, after reading the manual and seeing the schematic, I am really impressed. That parafeed thing is new to me, along with the power stage driver system. Who would have thought that preamp tube is actually for computer applications (as per the datasheet). It´s going to be a fun ride.
Will be doing inventory later today, checking for the necessary upgrade components.
 
Couple of questions, though:
How have you guys mounted the little driver PCB in your chassis? Nylon standoffs?
Same goes for the hum balance pots, I feel like attaching them to something more than just the soldering points of a tube socket. Glueing the backside of the pots to the chassis plate, maybe?




 
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