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RH84 (EL84) Choke etc...

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Would the GXSE 15w model offer any advantages over the 10w model? I'm thinking not, but if the frequency performance is based on 40hz at 15w then there is more cushion for performance at 3.5w?

It really depends on where your 'sweet spot' is with budget/performance.
Like 6L6, if given a choice, I'll generally go with the 'bigger is better' (or 'better is better').
I think you will be happy with the 10W, if you'd rather put the $20 upcharge for the 2x15w someplace else.

The RH84 is an excellent project, but not-at-all an 'ultimate amp', so just get reasonable parts and put it together. (I wouldn't bother with expensive 'audiophile' caps and the like either. I used a couple of Russian PIOs and the rest ordinary stuff from justradios and was happy.)

John
 
Yeah - that's one of the frustrating things about being a newby in audio DIY - so many choices and no consensus! (Understandably in some cases.)

Reason for building a Single Ended EL84 is that it will be replacing my single ended Miniwatt EL84, which has really impressed thus far. The miniwatt has a switching power supply and I can't find details on the output transformers, but I'm hoping to improve on it by using a similarly simple design, but with better components. If all goes to plan, then I'll sell the miniwatt and ponder what to build next.

I like the EL84 sound, though would consider maybe trying a direct heated single ended triode next. I will admit that I've been tempted to go straight to a DH SET and then just keep the miniwatt, but given that this is my first build I should probably start with something simple and relatively low cost...
 
\My question to you is why you decided on a single ended, pentode-wired EL84.

I'm not the one building the amp, but I can take a couple guesses:

It's a relatively easy, straightforward build.
Many people have reported building it with good success.
The required tubes are common, readily available, and reasonably priced.

Perhaps if he wanted the "ultimate" (?) amplifier, he could be looking at Koren's TENA?
 
Now you have me curious! What would be an ultimate amp build?

What 6L6 said....

My point was:
Just get going on this project- once you have it completed you will have a better idea of your 'next project', and then on-and-on.....

The RH84 is a good amp if you have reasonably efficient speakers. I liked mine and gifted it to one of my nephews. Built a Pointz (Audiotropic) Music Machine to fill its spot...

I see a lot of projects online that never get completed while the builder is accumulating a pile of expensive components. (paralyzed in preparation/planning)

I try to put myself a bit more in the 1950s diy style (improvise and get 'er done) and find it rewarding.

As they say , YMMV......

John
 
Now that I have the choke and output transformers settled....

I'm a little puzzled about the power transformer. The schematic calls for 600v (300-0-300) plus 6.3v x 2 for the filaments plus 5v for the rectifier circuit.

I can't seem to find transformers with the double 6.3v. I did find one at Edcor but it also has a 25v and goes for a fairly steep price: EDCOR Electronics Corporation. XPWR167-120

Hammond has the 372jx but the Hammond site seems to indicate that it only has a single 6.3v (vs Parts Connexion which seems to be worded such that it might be a double 6.3v)

If anyone can shed light on this it would be appreciated. I am a bit puzzled by the transformers because a lot of people talk about using old iron...but if it is so hard to find the right specs in even new iron then I'm not sure how they make old iron work?
 
Thanks. Out of curiosity - does anyone have suggestions for how to order the power transformer such that it could be useful for future projects down the road? I'm wondering whether to oversize etc?


If you do a decent job building it, you could probably sell your RH84 (down the road). That could generate the $$ for the next bunch of parts.....

Your parts box will tend to increase in size with time as well - dumpster diving and scanning CL for old hifi gear, will build up your collection of power transformers.
So my advice would be to get what you need for the RH84 and let the next project fend for itself, for now.
;)
John
 
Now that I have the choke and output transformers settled....

I'm a little puzzled about the power transformer. The schematic calls for 600v (300-0-300) plus 6.3v x 2 for the filaments plus 5v for the rectifier circuit.

I can't seem to find transformers with the double 6.3v. I did find one at Edcor but it also has a 25v and goes for a fairly steep price: EDCOR Electronics Corporation. XPWR167-120

Hammond has the 372jx but the Hammond site seems to indicate that it only has a single 6.3v (vs Parts Connexion which seems to be worded such that it might be a double 6.3v)

If anyone can shed light on this it would be appreciated. I am a bit puzzled by the transformers because a lot of people talk about using old iron...but if it is so hard to find the right specs in even new iron then I'm not sure how they make old iron work?

You might look into this budget outfit for a transformer. I have used a couple of these for this exact amp and they work perfectly, Bonus, dual 6.3V taps
TUBE PWR XFMRS - Musical Power Supplies Inc.- Quality Tube Amplifier Parts You CAN Afford


Part number PT325.2
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I am a bit puzzled by the transformers because a lot of people talk about using old iron...but if it is so hard to find the right specs in even new iron then I'm not sure how they make old iron work?

Sometimes you have to be a bit creative with the rectifier section to get the right B+....all part of the challenge.
For small amps usually old iron will provide enough amps on the 6.3v heater winding. It helps if you know what the power transformer was driving in its 'previous life'.

John
 
You might look into this budget outfit for a transformer. I have used a couple of these for this exact amp and they work perfectly, Bonus, dual 6.3V taps
TUBE PWR XFMRS - Musical Power Supplies Inc.- Quality Tube Amplifier Parts You CAN Afford

I've dealt with MusicalPowerSupplies in the past. It would probably be a good idea to drop him an email to confirm stock on hand. (Sometimes he has stuff that isn't listed on the website as well. He was trying out some 'HiFi' ideas 1-2yrs ago.)

John
 
You can always place a capacitor across the choke to resonate it. This will improve the ripple on the DC.

There's some info here: Inductors and Capacitors Together

Take your AC frequency and multiple by 2 if using full wave or bridge rectification, then work out the value of C. Pick the nearest preferred value and place in in parallel with the choke (don't use an electrolytic!). I always get three caps, one nearest the calculated value and one either side, then pick the best! Most chokes lose a little inductance when passing current.
 
The amp is built!

Sounds great - but I have a question. The edcor gxse transformers have a 40% tap for ultra- linear. Can I disconnect the screen resistor and use the ultra-linear tap instead? Or does the amp need more substantial modifovations?
 
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Can I disconnect the screen resistor and use the ultra-linear tap instead?

Absolutely. I would suggest keeping a small resistor in series between the screen and the UL tap. Something about 100 ohms, 1/2 watt should suffice. It helps protect the screens during startup while the power supply stabilizes.

With the UL connection, you will get less power out of the amplifier.
 
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