Kofi Annan in: "Push and Pull with Me"

[SY]

I haven't used the Hammonds, but buzz is that they're very good, not the best, but very good. Jones used surplus iron (IIRC, Leak). My amp uses old UTC jobs (wonderful), and I have also had good experience with Dynaco trannies (salvaged from SCA-35/ST-35).

Hopefully, someone with recent experience with easily-available transformers could chime in...

[Kofi Annan]

Thanks. Would the 1608 or 1650E do? Could I compromise on the primary impedance somewhat to have more choices on the output iron? If so, what are the liabilities for increasing / decreasing the promary impendance from the recommended 8K?

Tired of responding yet? You will be.

Kofi

[SY]

One of the nice things about EL84 is the degree of documentation. IIRC, Mullard even published charts showing the effect of load on power, distortion, and the like. I'll see if Mrs. Y will give me an opportunity to scan them and post (at the moment, I'm playing Mr. Mom with the youngest Y, who will NOT allow me to go into my lab).

Both the choices you mention should work fine. The 40% UL taps give you lots of flexibility.

[gingertube]

Kofi,
I used salvaged output trannies for my "Bervois Valley" amp as well. I can confirm a couple of things SY has said. Stick with the 8K Primary Impedance and 40% Ultralinear Taps (I actually ran a version with 6K Primary and 20% Ultralinear at one stage - it wasn't as good BUT then the trannies were half the physical size).
I also tried the Low Idle current version which is talked about in some old EL84/6BQ5 data sheets, that is using 470R Cathode Resitors rather than 270R. I preferred the 270R as per Morgan Jones schematic.

The "Bervois Valley" is ideal first push pull amp project - it was certainly mine.

I tried many NOS and new production tubes in the output and new production JJ Tesla EL84 were the pick of the lot, even out performing matched pairs of NOS 6BQ5. This stacks up with SYs experience.

I also used JJ Tesla ECC88 (6DJ8) but other 6DJ8s (BRIMAR) and ECC88s (PHILIPS) I had sounded no better or worse.

I used a solid state high voltage rectifier rather than a tube, initially with bog standard 1N4007 diodes followed by a 220uF/385V Electrolytic (single power supply for both channels) and then 47R + 100uF/400V feed to each channel. See notes below: diodes changed to ultrafast/soft recovery later. Watch this if you use a solid state power supply - you need 305 to 320 volts for the 285V High Voltage Regulator to work properly.

Mods to my amp - You may want to try some of these ONCE the AMP is built, tested and running.

- coupling caps changed to film/foil polypropylene
- Blackgate 470uF/50V Standard for bypass caps on the output tube cathode resistors.
- Global feedback reduced to 8dB, this will test your maths.
- rectifier diodes changed to Ultrafast, Soft Recovery (a noticable improvement)
- output tube cathode resistors replaced with "Ring of Two" MJE340/BC548 transistor current sources bypassed by the same Blackgate caps.
- 1uF/900V Polypropylene caps added to each channel from the output transformer centre tap (main power feed) to 0V at the point where the cathode circuit wire back to 0V
Best of luck with it.
Cheers,
Ian

[SY]

Mr. Secretary, you will find what you're looking for at the invaluable Frank's Tube Pages:

http://frank.pocnet.net/sheets/129/e/EL84.pdf

My suggestion is to give copies of this to Ariel Sharon and Mahmoud Abbas to see if they can come to a reasonable accord on loading. As a non-participant in their petty squabble, I would stick with 8K, but your speakers may dictate whether you use pentode, UL, or triode loading.

[gingertube]

And also, STC Application Report 6BQ5 (EL84) here.

http://www.retrovox.com.au/STC6BQ5.pdf

Page 5 has the data for Ultralinear Operation (11 Watts at 0.7% total distortion)
Page 20 has the graphs for Ultralinear Operation

Cheers,
Ian

[Jaap]

I am more or less in the same position as Kofi Annan, I am also a secretary-general (in my family) and I am going to build my first PP-amp soon. I have decided to build "Will's Amp" a design I found at Tube DIY Asylum. It is simple, it has the 6B4G (good tube) and I already have a LL1660 interstage.
After that I plan to build a variation of the Allen Wright Amp and also the Tabor of Gary Pimm is on my list. You see I am a bit like the communists I make 6-year plans. For inspiration I advice Kofi also to look at the designs of Lyn Olson.
And although the weight of all those transformers in my current SE amp have almost killed me (back injuries) I do think it is the way to go.

For al those projects you need a good Ausgangsübertrager (OPT). Financial funds are always a problem for every secretar-general. I just bought a pair of brandnew and very impressive looking 6K6 double C-core transformers in Eastern Europe for a very very reasonable price.
Do not even think of getting this quality for this price with a vintage part. I like to push the economy over there and at the same time look after my own business. This could as far as I know selbstverständlich also be the best way to go for Kofi.

Look here: http://www.korato.com/series.php?id=26

Of course no family or other political relations involved here. With a 6K6 you are more flexible than with a transformer for el84/6bq5. Although a el84 amp is excellent for a first PP amp I personally think my choice could be better for Kofi. I think this amp is more simple and should have better sound. You can reuse the OPT later for all kinds of great amps (with more power) while your EL84 OPT can anly be used with a 6V6.

What does the world community think of that ?

[Kofi Annan]

Whoo! Thanks for all the great information!

So, I've decided on the Bevois Valley for sure, despite Jaap's recommendations (sorry, Jaap). The BV amp is ridiculously well documented and it seems like plenty of people are satisifed with it, so there you go.

Tubes are one their way, courtesy of a birthday present from Kofi Annan Sr. and I'll probably order the remainder of the parts next month sometime (Mrs. Annan's birthday is coming up, so I'll need to drop some cash on the old lady), but I wanted some recommendations on flavor of parts.

First, is there any real difference between the Hammond 1608 or 1650E besides the output power? Would I be better off with the 1650E?

Both have UL taps, but I just wanted to know if the 1650E would be a needless waste of cash.

Also, in my last project (Thorsten's stereo pre), I used wirewounds as anode loads, carbon films as gridstoppers and Vishay and Holco metal films in the signal path. Any recommendations here? If you decide to recommend, I'd like to know WHY you prefer certain resistors in particular positions.

Finally, any case recommendations? I have used the top plate / wood box method before, but I wouldn't mind using a nice Hammod enclosure if anyone can recommend. I really suck at casework, so the minimalist approach is just fine.

See? And you thought you were done...

Kofi

[gingertube]

Some time ago I was in correspondence with Hammond seeking data to do some modelling. They sent me a spreadsheet with a lot of data on the entire 1600 Series Transformers. I actually intended to post it BUT how do you post an Excell Spreadsheet?

Hammond 1608 Data:
Primary Inductance 63.66H
Primary Current 84mA
Primary Voltage 283V
Primary DC Resistance 203.3 Ohms
Primary Impedance 8000 Ohms with 40% UL Taps
Secondaery Taps 4/8/16 Ohms
Secondary Voltage at 10W output 6.33/8.95/12.66 Volts RMS
Rating 10 Watts
Full Power Frequency Response 30Hz to 30kHz
Dimensions 2.5" x 2.79" x 3.06"

Hammond 1650E Data
Primary Inductance 63.66H
Primary Current 107 mA
Primary Voltage 348V
Primary DC Resistance 178.3 Ohms
Primary Impedance 8000 Ohms with 40% UL Taps
Secondary taps 4/8/16 Ohms
Secondary Voltage at 15W output 7.74/10.95/15.49 Volts RMS
Rating 15 Watts
Full Power frequency Response 70Hz to 30kHz
Dimensions 2.5" x 3.5" x 3.06"

The 1608 better suits EL84 Outputs in Ultralinear Mode (due to the lower Primary Voltage and Current) and has better low frequency response. That is, it is the correct choice for a "BV" Amp.

From the above I would hazard a guess that the 1650E is better suited to Triode Mode Push Pull EL34s, KT66 etc.

Best of luck with your "BV" Amp. A lot of us have built these things so just keep posting questions as they occur and we will do our best to help.

Cheers,
Ian

[SY]

Your resistor choices are quite sound (to make a pun). One other possibility is carbon composition resistors as grid-stoppers. In that usage, their flaws are irrelevant and their great virtue (low inductance) is exactly what's needed in that spot. Confession: I use both comp and film interchangeably, depending on what I have on hand...

Ian, does Hammond provide leakage inductance, capacitances, or anything else to sort out which transformer would have a better HF response?