EL84 Amp - Baby Huey

[jazzzman]

I called Antek. They were very responsive and easy to deal with. Francois, you are correct. They told me that the cover sits above the top plate and does not touch it. He also said that the cover is powder coated so there would be no connection even if it touched. I asked him if I could use a nylon bolt to give myself a little more confidence. He said I could, but that it was not necessary.
Francois, do you or anyone else have any further thoughts?
Thanks

 

[dBel84]

I used an antek cover on mine, no shorting, works perfectly.

 

[jazzzman]

Thank you, dBell84. The covers that Antek is currently selling are slightly different from yours. Now they connect to the chassis through a bolt in the center of the transformer.

 

[jazzzman]

Does anybody know the output wattage of the EL84 BH with the 23% taps (it is a toroidy transformer)? I am trying to calculate the rating for a switch to use to select between the output taps.
Thanks

 

[itsikhefez]

I would just use one of those NKK switches like this: https://www.digikey.com/en/products/detail/nkk-switches/S6A/1046694

In terms of output it kinda depends at which THD you consider the max output, but its likely somewhere in the 12W
For EL84 push-pull, the datasheet has it at around 15W for 20% taps and 11W for 43% taps
http://www.r-type.org/pdfs/el84.pdf

 

[zintolo]

Does anybody know the output wattage of the EL84 BH with the 23% taps

With a B+ around 330-340V and 30 mA you’ll get around 20 Wrms. Don’t expect them to be at 1% THD, but that amp is pleasant even at high volumes.

 

[zintolo]

For EL84 push-pull, the datasheet has it at around 15W for 20% taps

That’s with a B+ of 300V and UL only. I considered 340V with a stronger Schade feedback. With a 13% increase in voltage there’s circa a 39% increase in power, that’s the 20 Wrms I mentioned.

 

[jazzzman]

Thank you, both. It appears that a 6 amp switch should be more than sufficient.

 

[waltube]

For EL84 push-pull, the datasheet has it at around 15W for 20% taps and 11W for 43% taps

Agree.
The other numbers are comes from simulation I think, not from real test.
In class A p-p, pentode connection I got 10 wrms

The current on one 84 at 10 wrms

The pair

 

[zintolo]

All data you have got in this page, with different configurations, are right and confirmed by the datasheet linked above:

There will then be some variations due to the fact that:

• this amp is fixed biased vs cathode biased on the datasheet (means more power)
• this amp adds a-g1 feedback and the datasheet data don't (means lower THD)
• different voltage supply give different working conditions and so different power and THD.

 

[jazzzman]

I see some interesting looking transformers from Monolith Magnetics. They build one off custom transformers. Has anyone had any experience with them?
I am trying to fill out their form for a quote, but I have a question regarding the load on each tap. I would specify ac for the heaters, but rectified for the bias tap and the HT tap. How many dc amps should I specify for the bias and HT taps? Also should I have a separate winding for each channel or can I use the same winding for both boards?
Thanks in advance for any help anyone can give me
Here is a link to the quote form:
https://www.monolithmagnetics.com/sites/default/files/fillable pdf for custom power tranformer.pdf

 

[jazzzman]

The lack of response suggests that nobody thinks it makes any difference whether I have separate windings for each channel or one winding for both. Therefore, I will go ahead and order a single winding for HT, one for the power drive and one for the heaters for the stereo amp. I also assume that the ampere specifications are for stereo amp, not per channel. If anybody thinks otherwise please let me know.

 

[Francois G]

Sorry you did not get an earlier response. I'd say your questions were a little hard to answer without more context, budget etc. You are building EL84 with the on-PCB power supply, right?

I have not personally used Monolith, but they have a great reputation by all accounts I heard - rather expensive but very good.

Yes, you will get better separation between channels and probably stabler stereo imagery and dynamics if you have individual power transformers for each channel (mono blocks). Separate windings for the (HV) B+ of each channel on a transformer common to both channels will be slightly less so, but still better than having only one coil for B+ feeding both channels. How much better is hard to say/quantly and what the cost difference will be only multiple quotes from your supplier will tell. Then your budget will decide.

For a custom power transformer I would want at least 125 mA DC per channel capability for B+ (HV) . You could be OK with 100 mA but for a small difference in price you will pay the extra headroom will be nice. I don’t recall seeing the current draw for the bias but it will be a few mAmps, certainly less than 20 mA.

Hope this helps.

 

[jazzzman]

Thank you, Francois, that does help. It looks like Audiophonics is slightly more reasonably priced (although still more expensive than the off the shelf transformers mentioned in this thread). I like the custom transformer because I can get all the windings in one transformer, so I am willing to pay a bit more. I will check the prices of both options and try to make a decision.

 

[zintolo]

I've been conservative with my monoblocks (each trafo is indeed enough for both channels), because I installed them inside the chassis and I wanted them to run cool. In any case, those are the specs I've used:

TS 100VA
PRI: 230V
SEC I: 235V (250mA)
SEC II: 6,3V (5A) CT
SEC III: 55V (50mA)