Will This possibly work?

[Trout]

Gezz I am ambitious lately..

Anyways, I have another project started now, Want to use this for tape and CD playback.

The Million dollar question is will this work or even come close?
schematic

Looks close to me,, But hey,I am no designer, I just enjoy the torture building stuff in the 89 degree ,85% humidity we have been seeing all summer.

Gene

[Eli Duttman]

Problems.

For lowest distortion, screen grid B+ should be regulated. A VR150 should get the job done.

The O/P impedance of pentodes is HIGH. That means a LOW damping factor and poor voice coil control. Loop NFB is needed to lower the O/P impedance.

BTW, Eli is cheap. A $4 7Z4 instead of the 6CA4 is good for 100 mA. of DC.

[planet10]

Originally posted by Eli Duttman
The O/P impedance of pentodes is HIGH. That means a LOW damping factor and poor voice coil control.

Which is excellent if you want to do the current amp thing with some efficient FRs.

dave

[hacknet]

why not try some local feedback, theres been lotsa talk bout it and i`m waiting to try it.

[Trout]

Originally posted by Eli Duttman

BTW, Eli is cheap. A $4 7Z4 instead of the 6CA4 is good for 100 mA. of DC.

Eh, I have a dozen 6CA4's laying around of various brands, So to me they are a good choice, Plus, I have no loctal sockets laying around.
I am only looking for 4-5 watts tops here.
I am concidering NFB loop but I am really not up on how to modify the current schematic yet.

Hopefully I will have this built by friday night, Chassis is done and I am mounting sockets Trannies Ect already.
Once again I am packing this into a 6X10X2 Hammond chassis as I had several here to putz with.
Gene

[dr._sleep]

Down here in Louisiana 97 degrees/ 95% H, we DIY in the AC.

Here's nifty feedback circuit for the EL84 operating as a pentode. I don't think you'll care for the sound without NFB, something about the non-linearility at midband to high frequencies.



Looks like you're pretty close. Ignore the 4.7 ohm 5 watt to ground off the OT. Float the OT's without reference to ground.

Take a look at the Taboo circuit at www.decware.com under articles.

dr._sleep

[planet10]

Originally posted by hacknet
why not try some local feedback

After going thru a number of EL84 SE, we ended up with a variation on the RH84.... a couple fairly lengthy threads here covering that one.

dave

[Trout]

Originally posted by dr._sleep
Down here in Louisiana 97 degrees/ 95% H, we DIY in the AC.

Here's nifty feedback circuit for the EL84 operating as a pentode. I don't think you'll care for the sound without NFB, something about the non-linearility at midband to high frequencies.



Looks like you're pretty close. Ignore the 4.7 ohm 5 watt to ground off the OT. Float the OT's without reference to ground.

Take a look at the Taboo circuit at www.decware.com under articles.

dr._sleep

Now, 2 Dumb questions time, The 10K pot, #1 Is this an adjustment I will be needing to make often? Or #2 should this pot be easily accessible?

After going thru a number of EL84 SE, we ended up with a variation on the RH84.... a couple fairly lengthy threads here covering that one.

I did a search on that, Oh My thats alot of reading! 70% of which is brail to me, So I will need to study a bunch before going to far as I hate rewiring to much inside such tight chassis.
But I am sure the results will be well worth the efforts.
Gene

[Trout]

Just A Thought,

After searching a few RH84 treads, One recently used a simplier(to Me anyways) Schematic to achieve nfb.
Here



Given the chassis limitations and simplicity of this circuit, Wouldnt this give me about the same results?

Gene

[planet10]

Originally posted by Trout
Given the chassis limitations and simplicity of this circuit, Wouldnt this give me about the same results?

No

That is no simplier than the RH84. And the RH84 feedback is much more local.

In our experience, the global feedback pentode wired amp (as per your map) doesn't work as well as the same amp triode wired with no feedback, and that doesn't sound as good as wired RH-style. The RH also has twice the power as the triode version.

dave