36 Watt PT rating ?

[stevesuk]

Gabi,
Thanks for the 36W room

Can we discuss the Power/Output Transformer ratings ?
PT
6.3V heater current

4 X EL84s @ 0.76A (76mA) each = 3.04 A
3 X ECC83s@ 0.16A (16mA) each = 0.48 A
Total = 3.52A

5 Volt heater supply for GZ34 = 1.9A say 2A

300v ? centre tapped 200milliamps ?

Output Transformer

4K ohms Primary Impedance
tapped 4, 8, 16 ohm speaker impedance ?
Rated at 30 watts or more ?

Lets have your input chaps.

Steve UK

[Ingo]

Hello Steve,

I would like to see the 290 Volts for the anode voltages. The GZ34 has a lower internal resistance than the EZ81 and therefore the voltage drop isn´t as great as using the EZ81. I have wounded my power transformers for 300 Volts and it seems that the voltage is too high, so that you have to use two serial 100 Ohm Resistors between the transformer and the EZ81 for dropping down the voltage to nearly 290 Volts.

The 30 Watts Power for the Output Transformer is fine. It is the same power rating the original AC 30 Transformer from Albion was designed for.

Kind regards
Ingo

[jaysg]

I would like to see the 290 Volts for the anode voltages.

I don't build enough amps to know much about this. Why 290V? My 18 is at 348V. Is there some mojo to be gained by dropping that down? Just wondering -- also, Ingo, are you the guy with the great Mark Knopfler site?

[Ingo]

I would like to see the 290 Volts for the anode voltages.

I don't build enough amps to know much about this. Why 290V? My 18 is at 348V. Is there some mojo to be gained by dropping that down? Just wondering -- also, Ingo, are you the guy with the great Mark Knopfler site?

Hello,

there is no mojo. But it seems, that with some current productions of EL84s you can get serious problems. It is just to get the amp a little more safe and to let live the EL84s a little bit longer.

I´m not the guy with the Mark Knopfler sites.

Kind regards
Ingo

[Ingo]

Gabi,
Thanks for the 36W room

4 X EL84s @ 0.76A (76mA) each = 3.04 A
3 X ECC83s@ 0.16A (16mA) each = 0.48 A
Total = 3.52A

Steve UK

Hello Steve,

you shurely know it, the ECC83 has a current of 0.3A in parallel connection, so it would be a total heater current of 3.94A = 4 A

Kind regards
Ingo

[Gabi]

You are welcome guys!

I am sure good stuff will come out of here!!

gabi.

[nigelb]

The 5AR4/GZ34 has a drop of 17v, much less than a EZ81 which is about 45v. I used a EZ81 in my 18 Watt which with a 300-0-300 tranny gave 376v which is pretty much spot on calculation. With a 5AR4/GZ34 this would give 407v rectified. A 290-0-290 tranny will still give 393v. Which may be considered a little high. In my 18 watt I have used JJ and Groove tubes el84s at 376v with no problem, with a cathode resistor of 180ohm they are within dissipation limits, though I cannot confirm if the tubes will last a long time. Maybe you should be looking for 275 or 280v tranny considering the low voltage drop of the recifier.

But hey, there have been many amps like this built with B+ of over 400v. AC30's ran pretty close to destruction. The VVT VTH107 may just do if we want to run them this way, if not the Hammond 370HX will give a lower voltage. (Sorry US guys, thinking European suppliers here).

Hmmm...this new room is making me sit up and take notice.

[Plexi]

I think there are enough amps out there that you could go by..
Or use the transformer info.
To keep the amp true to being an 18,i'd like to have a tranny that gives the same voltage..just runs 2 extra tubes.. So the preamp and EL84s will keep the same voltage. If you look at the 18s.. the plate voltage is fairly high... but the screens are run at a lower voltage.. So you could also maybe use less plate voltage..and get by with upping the screens.
So you could have 300v plate,and 300V screens or a few volts less.
this can make a big difference. Just lots of things you could try.

I guess its good to compare voltages to a Vox because they use the same tubes..but hopefully when the smoke clears.. these amps will be different sounding than the Vox.. And even though marshall never made the 18 head version..they never made the 36 watt version either.
So it may be something very cool, you should be able to get more clean volume..and overall added crunch for playing live gigs..
Whos building heads..whos building combos..???

Richie

[jc]

The hammond 270HX PT and 1645 OT would work for the US guys.

PT 270HX 275-0-275 200ma 5 V@3 A ct 6.3 V@6 A ct
OT 1645 30 watts 5,000 ct 128 ma. 4-8-16-70V

with a 5ar4 you should get plate voltages in the 380 range.

[markh]

To keep the amp true to being an 18,i'd like to have a tranny that gives the same voltage..just runs 2 extra tubes.. So the preamp and EL84s will keep the same voltage.

I agree that we should keep the plate voltage about the same, but we'll have to make some adjustment for the lower impedance of a different recto (GZ34 or similar). I kinda like the 280v idea.

--mark

[Plexi]

Mark; while your here.. what are some of your ideas..??

As for the added parts.. layout etc.. I'm going to use a choke for my amp..and use 1 screen grid resistor for each pair of tubes..
Also the cathode resistor will need to be up in wattage some.
And add the extra grid stoppers.. Other than that,i want to keep mt amp as simple,and close to a stock 18..just only change a few things..hopefully to make it a little better. Whats your thoughts,or any other people like to share some ideas. Seems its not going to be much.. the main thing will be getting the right PT and OT.. As for the OT, theres more to it,than just 4k..
I know there are some good trannys out there.. west labs,OEI,list goes on.
But i wonder how they might sound compared to Heyboer doing them.
suggestions,comments??All ears here.....
Richie

[Graydon]

OK, I was talking to a friend of mine that calls on occasion to talk about amps. He has been reading here although I don't know if he will post or not. He told me that the really old AC30/4 used a PT that was only rated at 150ma! In other words, we might get away with using the original 18W PT! I will try that when I build my prototype just to see how hot it gets. You never know, maybe it will work!

[GlennG]

Heyboer makes a transformer set for the Trainwreck Rocket that may be worth looking at. Its a massive hunk of iron and I think the HV is 260-0-260 . With a GZ34 the B+ would be in the ballpark.


In the attatched photos the TW transformers are on the left and the 18 Watt set is on the right.

Glenn

[dboul]

Mark; while your here.. what are some of your ideas..??

.. the main thing will be getting the right PT and OT.. As for the OT, theres more to it,than just 4k..
I know there are some good trannys out there.. west labs,OEI,list goes on.
But i wonder how they might sound compared to Heyboer doing them.
suggestions,comments??All ears here.....
Richie

Hey Richie,

The RSDeLuxe (JTM45) OT has windings for EL84's. If you remember the amp that I built with that tranny, it was pretty special sounding. I bet that guy would sound great in this amp, especially when it sees 4k.

Just a thought . . .

[stevesuk]

I still have a few original RS 250 - 0 - 250V transformers with 220V, 230V and 240V primary taps, as the voltage in UK fluctuates around 236/7V I will try one of those and see what the output is. They already have 5V and 6.3V taps, which may need dropping a bit. I may use two in parallel like I did on my first ever 18 watt build to increase the current capacity.

Steve UK

[zaphod_phil]

I agree that we should keep the plate voltage about the same, but we'll have to make some adjustment for the lower impedance of a different recto (GZ34 or similar). I kinda like the 280v idea.

I have tended to think that running the amp at above 300V was an important element of the 18W sound. Don't you think so? IIRC that was one of the main differences between the 18W and the WEM Dominator, the design got ripped off from. I'm not really too comfortable with abusing EL84s with 340V and above, like happens in a lot of 18Ws. Maybe around 320V would be OK with you?

[Ingo]

To keep the amp true to being an 18,i'd like to have a tranny that gives the same voltage..just runs 2 extra tubes.. So the preamp and EL84s will keep the same voltage.

I agree that we should keep the plate voltage about the same, but we'll have to make some adjustment for the lower impedance of a different recto (GZ34 or similar). I kinda like the 280v idea.

--mark

Hello Mark,

The idea is, after looking around a little bit, the best compromise. Ok, the LEAK Stereo 20 wasn´t a guitar amplifier, but they reduced the voltages from 300 to 280 Volts, because getting problems with too high anode voltages. They used a GZ34 rectifier tube too.

Some words to Graydons idea with the 150mA anode current. Looking to the old Mullard Data Sheet, the PP connections needs for two EL84 a current of 2x46 mA for the anode and 2x11mA for the screen grids.

Kind regards
Ingo

[SteveinTempe]

Glad to see this new room..!
I am stuck in 4xel84 gear anyhow..
I am building that solid state marshall 2x12 into an ac30 top boost
but I would like to have one channel more marshall like...
because it has the cool basketweave and the big logo..
hammond 270-HX and salvaged output from the organ surplus
and a nice choke as well.
cheers and good luck going one louder..

[Plexi]

Very interesting replies.. I do agree,the amp and many amps out there today are running high plate voltages. The amp i have in the sound files was only a little above 300v... Most of the amps that run higher voltages,also have the screens running 15 to 20v less..
So if you did use 300v plate or there about..you could run the screens closer to 300v too.. And the choke would work good here.. But if you stick to the higher voltages..you still need to keep the other voltages for the preamp PI/Driver the same.. Quite a few ways that might work about the same..

Richie

[markh]

Mark; while your here.. what are some of your ideas..??

I've wanted to do a 36 forever, but my 18 watt mutant is still only half done!

As for the added parts.. layout etc.. I'm going to use a choke for my amp..and use 1 screen grid resistor for each pair of tubes..
Also the cathode resistor will need to be up in wattage some.
And add the extra grid stoppers..

I agree with all of the above...perhaps use two cathode resistors (one for each push-pull pair) to keep the wattage reasonable?

I know there are some good trannys out there.. west labs,OEI,list goes on.
But i wonder how they might sound compared to Heyboer doing them.
suggestions,comments??All ears here.....

Does Heyboer make an AC30 set? The Hammond 270/370FX or HX looks like it'd work (and be easy to get), and perhaps the 1645.

--mark