EL34 on a PCB?

[Shannon Parks]

The next project is a monoblock design that can be built as either a HF-87 (cathode bias) or HF-89 (fixed bias). Shots coming soon. One could be used as a guitar amp. A pair will wake up the dead on modern speakers (eg 89dB sensitivity). Just whetting your appetite. :twisted:

Shannon

[gogzhad]

What kind of iron does it need?

[Shannon Parks]

This is the current setup, but could change depending on what testing finds:
-Hammond 273BX for the PT. 700VCT, 182VA. Runs hot as the dickens- maybe I know how hot those Dynaco ST-70 PTs get now. :) EL34's set at 55mA.
-Hammond 1650P for the OPT - HUGE 60W trannies.

Angela has these for $50 & $61 respectively right now, so the pocketbook doesn't get hit <too> hard. The 1650P is actually cheaper than the 35W ones - for now. I'll post some pix in a bit.

Shannon

[EWBrown]

This is interesting..... Are you figuring about 35watts out? Not really familiar with the EICO amps (I have built some of their ham radio and test gear in the past). I would SWAG that tube rolling could be interesting here.

/ed b in NH

[gogzhad]

Hey Shannon,
I noticed that Angela Electronics has some Eico power xfmr's on their NOS transformer page. Would these be suitable for the Eiclone? Seems like it might be in the ballpark, except for the pain of making a cutout to 'submerge' the thing into the chassis down to the core (ala ST70).
And, a maybe somewhat dumb question - is there a disadvantage to having a slightly too large power transformer? In other words, if the B+ and other outputs are in the ballpark, is a too lightly loaded xfmr undesirable? Seems like you mention this in the blueboard assembly sheets with regard to the power trans selection between two different Hammonds...
tia,
dave

[Shannon Parks]

Hmmm,
Just looked at the Angela NOS Eico trannies - does the description mean it is a horizontal with no top cover (ie ugly)? Anyhow, the voltages are more in line with a heavy duty PT for the stereo 35 project (620VCT).
The eiclone project right now is running some serious B+ with the 273BX (700VCT) which can't be beat at $50. I've got a pair of huge snap mount caps rated at 385VDC in series at the input (ie 770VDC rating). I started taking power measurements the other day and my Eico 379 signal generator has a flaky sine wave output. :evil: Gotta fix it.
As for power tranny loading, I am no expert here but would now assume over-rating by a large amount (like > 100%) shouldn't be a loading problem for an audio amp (no comment on guitar amps as their power supplies factor heavily on their sound, eg sagging). My previous comments on the Hammond 272JX high filament voltage were based on the fact it was my first Hammond tranny. Now I realize Hammonds run high on the 6.3VAC taps. Granted, they are rated at 115VAC and I run them at 120VAC (don't forget the IRCL drop), but that is 5% over and I remember seening 10% over (6.9VAC) on the 272JX taps. Thinking out loud: now that I think of it, I wonder it I really did have the IRCL in when I did that test? I'll put that on my list of things to do. In the meantime, keep some dropping resistors handy just in case you ever need them.

Shannon

[EWBrown]

I saw an HF-89 listed on E-bay this weekend. If it is still there, I'll add the URL for it. Claimed 50 watts/channel, looked very solidly made. One of these would be a good source for output trannies, iand one power trannie, f it can be obtained on the cheap.

There are two listed, and no they are definitely NOT cheap!

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... gory=39783

and

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... egory=3284

The first (and more expensive) one is fairly clean looking, the second one appears to have been 'hacked" quite a bit.


/ed B in NH

[Shannon Parks]

Wow, Ed - I've never seen <one> HF-89 on Ebay, let alone <two>. I guarantee these will go for big $$$.

Shannon

[EWBrown]

I was surprised at the high prices these were getting on E-bay, even decent Dynaco ST-70s are less costly. And I always thought EICO stuff was considered as being "dogs". Oh well, live and learn.

I passed up on a Fisher tube amp at a local swapmeet. It used 7951As, and a friend of mine said that they were hard to find and expensive, (referred to them as "expensive fuses"), so I passed on it, even at $ 75. Later, I found on-line a simple re-wire mod to make it accept 6L6s or 5881s, just move two connections on each output tube socket, and change the cathode resistor values.

If it is available at the next swap, or if i find another one, I'll probably go for it. If anything, at least the trannies could be salvaged and they are worth that price.

/ed B in NH

[EWBrown]

The first EICO HF-89 is already up to $450. :shock: :?: :shock:

Second one which looks like it has had a rather sad and hard life is up to $315. Ouch!!!!!!! :shock:

Even a couple of HF-20 mono amps (6L6, 20-25 W out) are going for over $100.


/ed B in NH

[EWBrown]

Are you still going with the aforementioned Hammond trannies? I may order a couple of sets from Angela soon, and no, I won't bother with HWT, I could be very old befopre they arrive

Just getting ready......

/ed B in NH

[Shannon Parks]

Hold your horses, Ed. :)
Seriously, I'm probably going to make a couple changes on the PCB before I order anymore. At that point, I'll probably order 20 boards, ie enough for 10 pairs, and see who wants them (at cost). I started thinking of rectifying the 5VAC taps for the 12AX7 and 6SN7GTB. Then I decided, if I have DC, then I oughta have a small fan inside the unit to help keep the heat down. Any thoughts on this? I would choose the quiet 40x40mm fan and high CFM isn't an issue - just a little air flow should do the trick. Comments appreciated.

Shannon

[EWBrown]

If you're using DC for the filaments, having a 6A (or higher) rated FWB, just heatsunk to the chassis should be good enough, if you go for regulation, then either sinking the pass device to the chassis, or an internal heatsink with a small CPU fan should work.

I've seen it advised, if you run the filaments DC, reduce the voltage level around 10%, use 5.7 VDC for 6.3V tubes, 11.4 for 12.6V, etc.


So, what is the tube lineup? 12AX7, 6SN7, 2X EL34, and 5AR4/GZ34 (or solid state) rectifier (latter assuming you use 5VAC to rectify to DC) ?

I've been "loading up" on EL34s, to fix the old Dynaco ST-70, for the Eiclones, and a "Dynaclone" I'm planning on for next year.

That would basically be a set of Dyna ST-70 replacement trannies, an unpopulated ST-70 chassis amd cage from E-bay, and I already have a spare "upgrade" PCB. ANd a choke for the power supply.

If the chassis is too grungy and rusty, it can be either painted, or cleaned up and sent off to a motorcycle parts shop for chrome plating.

/ed B in NH (still screwin' off instead of workin')

[Shannon Parks]

Yeah, Ed - I'm going to put a FWB in there. It's rated at 4A 50v and 200A surge - should be good enough considering the 1ohm (or thereabouts) resistor past the huge filter cap (10V, 3300uF ?). I'll have to read the datasheet to see how long of a surge it can really handle or I need to use a bigger (6A or >) like you mention. I'd just <hate> to use a monster in there!
Served by DC: 1/2 a 12AX7 and the 6SN7GTB = .75A @ 6.3VDC
I did a lot of the layout this weekend - I gotta get moving on this!
Shannon

[EWBrown]

You might want to use one of the lower resistance ICLs if any are of the right values and ratings. 750 mA continuous, when the fillies are hot, I don't know the cold resistance, but a 1 ohm resistor should limit even a dead short to under 5A taking in consideration for winding resistance and
1.3-1.4 V diode "drop".

A long time ago I glommed onto a few 25A FWBs at a local hamfest, these are in a roughly 1.5" square aluminum body, with 4 tabs for push on lugs, and the diodes are encapsulated in black epoxy. These are almost indestructable, I think most transformers would give out before these beasties would. Mounting is simple, a hole in the center, large enough for a #8 screw, a little silicone heatsink gunk between it and the chassis, and it is good to go. These bridges are also available at most of the electronic stores like Jameco, All Electronics, Marlin p Jones, etc. for reasonable prices, if you want 'em in quantity.

Somewhere in my "better stuff" junk box, I also have a Dale 1 ohm 50 watt resistor, that also chassis mounted would handle just about anything I could throw at it.


/ed B in NH