Hammond 1650P vs 1650N For EL34 PP

[MVZIK]

Hi,

I know there are lots of discussions about these trannies but non really answered my question so I write in to seek some help. Will there be an audible difference using the 1650P(6.6k CT) which are less favorable in the EL34PP application comparing to the 1650N(4.3k CT). Also I heard the "P" will give out lesser watts with EL34 comparing to the "N" how much lesser? Thanks.

 

[TonyTecson]

if you connect your 8ohm speaker to the 16ohm tap, you will get more power as you end up with 3.3k reflected load at primary....

 

[MVZIK]

1650P for EL34 PP Amp

Thanks Tony,

someone built the amp for me using the P and I later found out that the N is actually more cut out for EL34. However I think the P are more for KT66 and 6L6which I will try out later. Now am using Sovtek 6550E. Generally I don't really find anything bad so far just wonder what the sonic difference would be if I were to have the 1650N. Apart from power output what other negative effect will there be because of this "mismatch"? Tks.

 

[TonyTecson]

or kt88/6550 using the 16ohm tap....

 

[TonyTecson]

are these hammonds easy to get in singapore?

 

[MVZIK]

Yes, there's a shop carrying it. Do I need to change anything in the circuit if I were to change to 16 ohm tab? Side tracking alittle I just finished building my B1 buffer preamp followed everything on the PCB and the schematics powered it up and the LED was on for a few secs and then when off. I'm using a 19v 880mA wall. 2 parts I'm not entirely sure are the D1 diode, I'm using 1N4004 which is printed on the PCB that opposed to the 914, secondly is the value of the LED, is 12v ok?

 

[roline]

I've tried for the 6L6 family; 6P3S, 6P3S-E 5881, EL34, Svet 6550=C= , KT88
Sweep tubes; 6JN6, 6JM6, 6CV5, 6LB6 and 6LF6 tubes all with the 1650 P iron.
For my ears, speakers ACI Orions ~3ohm connected to 4ohm, and listening room, triode mode sounds the best.....
A little less power, but more class "A" headroom. More than enough power for the speakers and listening room. 40 or the 60 watt sound about the same. I'm currently working on a ST70 like clone with old Hammond 6.6k 40watt iron, 6P3S-E 5881 output tubes. The bass in Annie's "Bare" CD is a worthy experience.
The 1650P appear to be great iron being able to be driven from most output tubes. If you are after more power don't forget the the 1650R 100 watt 5K version...... almost the same price...

 

[MVZIK]

Tks Roline nice tubes indeed. Have you tried KT66? I think they will sound great with the P. Why did you opt for P rather than N for you design?

 

[roline]

When I started to design tube amps I found an interesting graph of class A vs AB output power. I wanted a compromise with a larger class A operating zone without giving up too much power. I wanted a universal transformer that I could drive with an assortment of output tubes. My concern was the output impedance. The higher the Ra, the larger the iron impedance needs to be. Thus a decision was made on 6.6k.
I design 2 different platforms, sweep tubes and the 6L6 family.
Both are PCB based, just because I find it easier and it works great! I goal was to design amps that others could make by the toner transfer method.
A pic of the little Russian 6P3S 6L6 tube at 360 VB+ with a little blue glow..

 

[MVZIK]

Hi Roline,

Have you used the 16 ohm tab to connect to an 8 ohm speakers? What's the pros and cons doing that? Do you need to change your circuit if you change the tabs? tks.

 

[Bigun]

I was helping a friend develop an amp, a SE sv-811. Actually, all I did was to listen to different configurations. But it gave me a chance to hear different output tubes playing through one of these large Hammond OPTs with a 6.5k load impedance for the tubes. What I found was that on a 6C4C (2A3) the sound was very good - the bass was very impressive. Seems to me that the higher impedance (compared with what is usually recommended for 2A3) was very beneficial to the l.f. sound - perhaps because of better damping factor. I also heard the same tubes through the Hammond 125SE and then I realized why it's worth paying out for better iron.

 

[Salectric]

The 1650R works great with EL-34s. I haven't tried the P or N versions.

 

[MVZIK]

R got 5k CT and that should be quite a good match for EL34. and with 100w capability the amp will fly. I do heard that a little higher in impedance do have it's benefits sonically but don't understand why? A member suggested using 16 ohm tab for 8 ohm speakers and that will definitely bring down the impedance to 3.3k which is quite a comfortable region for EL 34 and KT 88 and allow higher power output, if that works, the P will be a very flexible OPT and I can switch the tab back to 8 ohm when I want to use 6L6 or KT66 but I'm not sure if there a need to make alteration to the circuit. Can anybody offers some inputs on that?

Hi Bigun thanks for your input btw what is I.F. sound? Also how much do you pay for 1650R in Canada?

 

[TonyTecson]

i think Bigun meant low frequency sound...

using the 16ohm tap for more power, you can also move the feedback resistor to that tap, you may increase it slightly.....

this is my EL34 pp amp, using russian 6J9 as input tube and 6CG7 as ltp drivers.....circuit culled from Mullard 5-20, Harman Kardon Citation5 amp circuits.....

what makes my build different from others is the use of common mode choke forming part of filtering circuit.....another is the generous filtering, each channel is separated by 3amp diodes, 500uf filtering caps each channel, use of single coil fwb circuit so that transformer heating is lessened compared to center tapped....about 500ufd is also used before and after the common mode choke.....

filaments are biased by dc at about 50volts to minimize hum and noise.....

 

[TonyTecson]

i think that Hammond and Edcor and other traffo makers should make the hv coils in their traffos as 2 separate coils, so that users have the option to series those for center tap rectification, or parallel for full wave bridge using silicon rectifiers in conjuction with tube rects.....

 

[roline]

Remember that a PP amp driven into class B operation, that one tube is doing the work. In that case the entire impedance is on that tube as Raa/4 so a 4.3K transformer would act like a 1K load..... Most commonly used output tubes will exhibit higher distorsion with a low load, so I prefer a little higher impedance, the 6.6k and not driven so hard.
Do a search on Turner audio, he has a great tutorial on this.

 

[TonyTecson]

Yagree, lower loads while increasing power also increases distortion, so it is really up to the end users to decide what he wants....just be aware of the options....

 

[MVZIK]

Hey Guys, got another question. 5k CT at 30hz vs 6.6k CT at 1k hz which is higher? When the 5k one reach 1k hz what would be the impedance? same, increase or decrease? Nice amp Tony, clone ST70? Mine got the input infront too but running 3 x 6sn7. Hytron in the middle and 2 RCA as phase inverters. EL34, KT88,77,66, 6L6 can be used as out-put tubes. Will figure out how to upload pics.

 

[TonyTecson]

opt's have higher power ratings at 1khz as compared to 30hz, reflected impedance is another thing....

mine is not an ST70 clone, it was a cull from mullard 5-20 and harman kardon citation 5, and all irons used in my amp were hand-built by me....the opt i used has a 1 1/4 inch center leg core, the st70 used 1 1/8.....