• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SRPP linestage help

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Hi all,
Following discussions on another thread of mine i thought i'd start a new thread. I have built (last night) an ECC88 based SRPP linestage as the atached schematics but with 0.6uf capacitor instead of 0.68uf and running 180V B+.

I am very pleased with this linestage so far, it sounds great to my ears. Only problem i find is that it has too much gain. On the other thread (which was about a psu for a paralell ecc88 linestage hence i made a new thread) i had a coupel of sugestions how i might go about gettign around this problem. as follows:

Eli Duttman said:
90 V. on the plate is "textbook" for the 6DJ8. 180 V. B+ looks GOOD to me for a 6DJ8 SRPP.

You can turn the excessive gain to your advantage. The Rp of the ECC88 is low, which makes it good for driving a trafo. The MagneQuest B7 trafo in the 5:1 ratio would reduce the O/P voltage by a factor of 5 and also reduce the O/P impedance by a factor of 25. The B7 also comes in a 3:1 "flavor".

While we are on the subject of "iron", you might want to look into a "tweak" developed by Australian DIYers. Choke load the SRPP .

Williams Audio said:

The over gain problem is critical only when is a noisy
output, but if you like to reduce the gain just a simple voltage divider will do it at the main or selected input of the amp.
best regards

I was just wondering what the advantages / dissadvantages of each method would be. Also i cant find a source for those suggested transformers here in the uk so was wondering if either of these would be suitable substitutions ?
Sowter 9041
Sowter 4383

many thanks in advance,
The Sowter model 8940 (spec sheet) is suitable. Cap. couple the trafo to the cathode of the top triode. A good sized cap., say 10+ muF., is needed. Don't be shy about sending Brian Sowter an EMail asking for help. The man is QUITE helpful.

A resistive voltage divider at the I/P is inexpensive. 1% metal film parts totalling 10 KOhms are in order. The tap gets connected to the line stage's level control. If your source(s) can drive a 10 KOhm load, it's a decent low cost solution.

A trafo in the O/P circuit maximizes S/N behavior and improves drive capability. Also, the trafo's secondary can be arranged to make the unit non-inverting.
I dont know how i managed to miss that one, i'll order a coupel of them on friday after i get my paycheck
.o0(thats this weeks paycheck gone, lucky i have my student overdraft i can live off)

I'm not too keen on trying the voltage divider on the input as i like to be able to plug my mates ipod's and creative jukebox mp3 players in when they come round and i'd like to be able to just plug anything in without haveign to worry if its going to work or not.

Thank's for being so helpfull, I'm still learning when it comes to tubes, im in university now studying my HND in electronics engineering but tube's isnt something we really cover apart from being told they exist and "aren't really used anymore" Pfft! shows what they know...lol. anyway, i'm sure i'll have more questions after i get the transformers.

thanks again,
just been lookign at the specs sheet and it looks a lot like the 9042 except the 9042 has a feedback winding and is center tapped. would it not be possible for me to use a 9042 (same spec sheet as 9041) and just ignore the feedback windings and the CT or would this cause problems?
i just ask because they are cheaper than the 8940 and im a cheapskate (should read: i'd rather spend the extra £20 on alcohol if i can get away with it. lol)
:rolleyes: students eh!

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