Should be good with a parafeed output. You could model it on the Hagerman Tuba. Good value Hammond transformers. I've tried the 157G myself and it works fine as a plate choke.
Tuba - Vacuum Tube Headphone Amplifier – Hagerman Audio Labs
Hagerman Audio Labs "Tuba" | Headphone Reviews and Discussion - Head-Fi.org
Tuba - Vacuum Tube Headphone Amplifier – Hagerman Audio Labs
Hagerman Audio Labs "Tuba" | Headphone Reviews and Discussion - Head-Fi.org
The 3A5 has a maximum plate current of 5mA, so let's say you would run one 3A5 per channel and just parallel them.
I would run them at 130V/8mA per tube, Rp of the each paralleled tube will be about 5K.
So this would leave you needing a 10K-15K transformer, then you'd have to talk about what headphones you want to power, as you may need to aim for something pretty specific. You will wing 42V RMS on the primary of a 15K output transformer at that operating point, so that's 1.2V at the output of a 15K:8 transformer. That is going to suck terribly on many headphones.
A 15K:150 is a nice idea, especially if it's a 150CT so you can have two different secondary options.
Parallel feed is a good idea. 250V of B+ would be adequate. CCS loading isn't much of an issue since the quiescent currents are low.
A 10K:8 transformer 1
I would run them at 130V/8mA per tube, Rp of the each paralleled tube will be about 5K.
So this would leave you needing a 10K-15K transformer, then you'd have to talk about what headphones you want to power, as you may need to aim for something pretty specific. You will wing 42V RMS on the primary of a 15K output transformer at that operating point, so that's 1.2V at the output of a 15K:8 transformer. That is going to suck terribly on many headphones.
A 15K:150 is a nice idea, especially if it's a 150CT so you can have two different secondary options.
Parallel feed is a good idea. 250V of B+ would be adequate. CCS loading isn't much of an issue since the quiescent currents are low.
A 10K:8 transformer 1
15K : 600 (150R Center Tab 2 groups) Hence it will be lowest at 75R by parallel 2 groups of 150R. My headphone is only 50R. So I can increase 25R by serial 25R resistor to my headphone to make it 50+25 =75.
Other schematic of TUBA still the same? even I replace EL84 with 3A5. except change OPT from 600R : 8R to 15K : 600R. Am I correct?
Other schematic of TUBA still the same? even I replace EL84 with 3A5. except change OPT from 600R : 8R to 15K : 600R. Am I correct?
When you finish your war with transformer thingie go for filament bias. I use paralleled 3a5 (both triodes in a single bottle) at 103 volt 10ma (5ma+5ma) parafeed output and get excellent sound. Please don't give up go for it. 3A5 will give you lot of trouble initially but if you can manage it will be rewarded with audio nirvana. Pay enough attention with power supply or it will be garbage in garbage out.
Regards
Regards
Thank you very much mr. minhaj. Now i will try to study about how to make good2.8v and 135vdc for 2.8v I might use LT1963 to control it but 135vdc need further study. I might search examples in websites and modify to get 135vdc
After use 6n23p and 6080 OTL HP AMP for long time. I wish my new3A5 SE Parafeed will sound better
After use 6n23p and 6080 OTL HP AMP for long time. I wish my new3A5 SE Parafeed will sound better
Dear Supernut
3A5 is totally different animal than your 6n23.. and 6080. 2.8 v i.e series connection with DC voltage source no good for filament heating. Please go for parallel connection with 1.4 volt, minimum voltage reg followed by ccs for the filament. Each triode of 3A5 is .5 watt dessipasion so 135 plate voltage @5ma current is .650 watt this way you burn your dht quickly. Please consult the data sheet and choose your OP accordingly. Modifying HT supply from another circuit for DHT family pencil tube like 3a5 will not work I think.
If you read the famous 26 preamplifier thread at this foram you gather some idea about the challenge. Best of luck.
3A5 is totally different animal than your 6n23.. and 6080. 2.8 v i.e series connection with DC voltage source no good for filament heating. Please go for parallel connection with 1.4 volt, minimum voltage reg followed by ccs for the filament. Each triode of 3A5 is .5 watt dessipasion so 135 plate voltage @5ma current is .650 watt this way you burn your dht quickly. Please consult the data sheet and choose your OP accordingly. Modifying HT supply from another circuit for DHT family pencil tube like 3a5 will not work I think.
If you read the famous 26 preamplifier thread at this foram you gather some idea about the challenge. Best of luck.
Why? If you put a resistor across each half of the filament, there's no issue with series connection.
There was a suggestion for 100V/10mA and 130V/8mA per tube (paralleled halves)
Hi Audiowize,
Point no.1
Agree about series heating, but I felt it would be little cumbersome for Supernut. Also you may use a single D cell battery if need be. I worked with 3a5 for a while and it is not a easy DHT to tame.
Point no.2
130 volt at 8ma is fine. But 100 volt at 10ma is little more linear. Also 15k primary will be better in terms of linearity and low end handling. I have no experience about driving a headphone though.
Regards
Point no.1
Agree about series heating, but I felt it would be little cumbersome for Supernut. Also you may use a single D cell battery if need be. I worked with 3a5 for a while and it is not a easy DHT to tame.
Point no.2
130 volt at 8ma is fine. But 100 volt at 10ma is little more linear. Also 15k primary will be better in terms of linearity and low end handling. I have no experience about driving a headphone though.
Regards
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