DIY Audio Projects Forum

Interestingly enough, in the last page or so of the Forewatt thread in the forum, there was a DIY'er with a similar hiss problem in his preamp. He fixed it by replacing the LR8. Maybe a bad batch of them are out in the wind?

I am listening to the KT88 OddBlocks after I fixed the noise issue by removing the LR8s, cranking it up (the room is shaking) and I got to tell you, they sound amazing!!! I cannot hear no distortion whatsoever. The addition of the sub outputs was also a great mod for when playing hard rock. Classical, jazz, easy listening, strings...it all sound great.
Besides the noise issue, it looks like the malfunctioning LR8s were also affecting the sound quality. It is much tighter, definite and clear.
Again thanks to all for the help. I am so glad!

works!!! the sound is very beautiful...when engage the feedback switch,the volume is a little higher...is normal? if the answer is no,what i have modify? the kt's 88 are setting within 87 ma each,485 v dc... thank you all...

Hi, if the sound goes up when the NFB is active the phase is backwards and you are losing a lot of the bottom end and the distortion will be higher. It should go down when the NFB is active. There are three ways to correct it. The easiest often is to swap the signal feed from the driver stage to the alternate output tube. The would mean unsoldering the two capacitors (what ever size you used ...0.22 to 0.47uf) and connect the signal output from the driver to the other tube. Then connect the second capacitor to the former active tube. This will feed the signal into the what was the slave tube and make the former active tube the slave. Alternatively if you only use one output impedance you can unsolder wires from the output transformer and swap the ground and hot ones. Be sure not to move the NFB and circuit grounds though. The third way is to swap the (with Edcor transformers as others may color code differently) blue and blue white wires and and the brown and brown whites ones from their original tubes to the other one in the pair.

EDIT, nice looking build....I do have concerns about the LM317s inside the amp like that though. They generate a goodly amount of heat and can harm other parts like capacitors. A lot of vent holes or slots above and below may be a suitable solution.


Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

hi Bruce!!! thank you very,very much!!! i do your first opition,inverting the capacitors,now the amp is all perfect!!! nice,nice sound...one more time,thankyou very much...may god bless you.

Hi,

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

The amp is very stable,marvelous sound...spend many hours today listening...the kt's88 with 60 ma and the negative feedback engaged are a very solid sound...

I make a mod in my stereo oddwatt,just add one more lm 317hvt in parallel,here in brasil is very hot most of the time,with this mod the lm's is working more cooled,the sound is beautiful,im in falling love with this amp...

Hi, that is an OK mod. I do that in the KT120 design. You would think that a pair would not work well together, but they do. Normally you would expect to arrange some sort of circuit to insure load sharing, but apparently these guys don't mind. A good heat sink on a single 317 is good for over 100ma per tube without stress. That is all I use in the commercial amps. The dissipation varies, but is in the 7-9 watt range depending on the bias point it establishes for the tubes. That will vary a bit from brand to brand and lot to lot.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

Hi Bruce,

Firstly most sincere thanks for what you have created in the world of tube amplifiers and everything that it has and continues to mean yo me.

Attached are a few pics of my version which fundamentally follows your design with a few minor variations.

The two Oddblocks are running without glitches now and the sound is just beyond rewarding.

I am a complete novice when it comes to building tube equipment (first time ever) so this new experience took me while to bring to where it is now.

LM317's are mounted each on a small heat sink with a small 24v fan running on about 7v just about inaudible. They are running at about 70 deg.C one on each channel with the other idle? at ambient temp.

Initially I opted for some Time Delay Relay tubes and later decided to use Omron adjustable TDRs .... same socket with minor wiring change. Later will enclose the TDR's and 'duct' the LM317 cooling fans... perhaps to be a touch more efficient with airflow channeling.

Upgraded from KTY88's to KT120's today without 14 ohm resistor addition (awaiting delivery)

Findings:
BIAS ... 43v
Current: 92mA
Tube Ext temp: 170 Deg.C
Plate Voltage: 468v
Diiferential Voltage: Pins 3-8 = 415v

Note: On the underside picture you will note that I have screened the .33uf PIO Cap on the V2 pin #5 to ground ... earlier had difficulty with fluctuating BIAS current. I suspect that as result of not building these amplifiers in an enclosed metal chassis I found that these caps were extremely sensitive to touch (me acting as some form of antenna?) BTW I tested them to highest possible extent on my Sencore tester without any anomalies detected.

Any comments/questions welcome and many thanks to all that shared and contributed which helped me tremendously.

Next project is the ForeWatt ...