Question on AO-24157-1 Hammond organ PT

[dude]

This PT from an AO-43, specs are 3A on the 5V sec.  A 5AR4 which is rated at 1.9A is usually used in 6V6 Plexi amps, I have several 5U4's I would like to use instead of the 5AR3 which are rated at 3A at the 5v sec. Since this tube was used in the original AO-43 layout, (2) el84, 3 12AX7, and the 5U4. Any good reason not to use a 5U4 in the Plexi's, the PT's 5v is rated at 3A so I'm good there?


Also, 1.8A rating on the 6.3 filaments (parallel), each 12AX7 current draw .3A, so the three 12AX7s are less then 1A, the 6V6 filaments .45A ,so seems with 6V6s the 1.8A, good to go. If I use 6L6s, .9A or double the 6V6 and EL34s 1.5V. Are these ratings in tube data for two power tubes or one?


Does all this mean if I use 6L6s or EL34s with this PT, in a plexi am I overloading the PT...?
And can I use the 5U4's with 6V6's and not stress the PT?


Never was clear on this applied data.

[shooter]

EL34s 1.5V. Are these ratings

for ONE tube

[sluckey]

Also, 1.8A rating on the 6.3 filaments

Where did you get that number? That PT on the AO-43 chassis also must supply filament current to the Precussion amp and Vibrato chassis. So, adding up all three chassis plus a .15A indicator lamp, that PT must supply 4.37A in total. I bet the 6.3V winding is actually rated for at least 5 amps.

[dude]

Well thank you Steve, yeah that PT also supplies the reverb unit. I got the info in another forum from a post, don't believe everything you read...


So the problem with that PT isn't with the filament current draw but the power tube draw. That forum post also said that PT is rated at 160 mA..., true? What does that actually mean in regard to using 6L6s or El34s?


The only A043 iron to Plexi I build runs cool to the touch with 6L6s and El34s after a few hours of loud playing..., just don't want to sell a friend a Plexi with that PT and EL34s and have it fry.... Also, I take it that PT can handle a 5U4, I assume the dropping voltage might be different though.




al

[sluckey]

yeah that PT also supplies the reverb unit.

The AO-43 ***IS*** the reverb unit plus the power amp. The schematic has 160mA written on it down in the power supply. But it's written in such a place that it's hard to say if that means there is 160mA total load current flowing (this is what I think) or does it mean the PT max current is 160mA (I don't think so). You could very easily measure the current drawn with one of your 6L6/EL34 Plexis. Just install a 1Ω resistor between the rectifier tube and the filter/load section. Then measure the voltage drop ***ACROSS*** that 1Ω resistor. I really suggest you do this anyway since you may be stressing that PT. It's more usual to see a PT rated at 200mA or more in big bottle amps.

We know that PT can safely supply a cathode biased 6BQ5 amp. And that means it can also safely supply a 6V6 amp. I've always tried to use iron in circuits that present a similar load as the original circuit. You are effectively doubling the load by using your big bottles. Can that PT handle it? 

[st]

Additionally, note that while the 5ar4/gz34 and 5u4 are often interchangeable, they will produce different b+ voltages, which Will effect how your amp operates (but not necessarily in a bad way...) See the following chart linked to in this thread: https://el34world.com/Forum/index.php?topic=20455.0

[dude]

Thanks for all the info, if I run EL34's, disconnect the lead from rectifier to first filter cap with a 5 watt, 1 ohm R, that's going to tell me the current draw with El34s but since I don't know the rating of the PT, what am I looking for?  I agree the specs on the schematic most likely is the current draw with the stock tubes, (el84s) and not the overall rating of the PT.


I guess, measure the current draw across the 1 ohm R with EL34s, hopefully it's not much over 160mA, feel if the PT is hot, warm or cool as I still don't know the rating. I'm sure if it's 160 mA with EL84, it's going be to 200 mA or more with EL34s. So the feel test? Seems like a flimsy way to check rating, am I out to lunch here,


The 5U4 probably would be ok for 6V6s but probably too much voltage drop for 6L6 or EL34s. 




al   

[sluckey]

If you are building this for yourself, put whatever tubes you want in it. If you're building to sell put 6BQ5s or 6V6s in it and tell the buyer these are the only tubes that will run safely in this amp. You have full control. The only way to know what the current specs are for that PT will be to contact Hammond. They will likely tell you that the PT was capable of powering a L-100 organ just fine.   

Use at your own risk but my advice is to not put big bottles on that PT.

[dude]

Yeah, sounds good, 6V6s.


I built one for myself, all my jamming buddies flipped over the amp once I got it sounding good with 6V6s. For me and most of my buddies, 6V6's in that amp is plenty loud for a small to medium size place we'd play, my guess is that 6V6 Plexi puts out out probably 22 watts with 6V6s.


Amp sure have a lot of balls with 6L6GC, PT never got hot or even warm with 6L6s or EL34s but very loud, beefy and great tone, even bias on the hot side. Then I have to beef up the OT, costing more... I never played a November Amp but EL84s don't have the low end 6V6's have, they are too chimney for that Amp, IMO..
I'll stick with 6V6's.


I have eight AO43 chassis's now, I will sell them to my buddies and their sons but take your advice and recommend 6V6s only.


Last thing before I start building these, I don't have any 5AR4s, the cost for all these chassis's, tubes and parts is over a grand (used old stock tubes) so I'd like to use the five or six 5U4's I have here. Tube data says 6V6s don't need 415v on the plates, if I use the 5U4s I'll drop 40/50 volts, instead of 20 with 5AR4. I guess I might lose some headroom, tightness or tone with lower voltage?     

[sluckey]

Deluxe Reverbs have been running 415V on the 6V6 plates for 60 years. They like it. I would not count on the 5U4s dropping as much voltage as you might think. 5U4s will work fine in that amp. That's what came in it. The main reason I prefer 5AR4s is the fact that they take about 15 to 20 seconds to warm up and put out any B+. 5U4s will be up and running in less than 5 seconds.

[PRR]

> lead from rectifier to first filter cap with a 5 watt, 1 ohm R, that's going to tell me the current draw

The waveform in the lead from rectifier to fist cap is VERY spiky. Most meters will not give a right reading.

Surely you installed 1r cathode resistors?? Then you know the EL34 total current. Little bottles don't count for much.

[dude]

5u4 has a directly heated cathode, 10 sec it’s putting full voltage to the filter which isn’t warmed up yet, would this put a voltage rush on the first filter? The B+ would be about 425v, I’m guessing the fast surge might be over the cap rating for a few seconds...? I have a can cap, 50uf @  500v. I’m not going to blow that filter with a 5u4 at start up, am I?


I have a few 5v4’s, maybe that would be a better fit?

[sluckey]

Filters are passive devices. They don't have to warm up.

[PRR]

Measure the turn-on peak voltage.

However electrolytic caps won't blow-up in 11 seconds, and you can typically take a 20% over-voltage at turn-on.