HF-85 Rebuild advice

[barchetta]

So after removing the can capacitor I can see its blown (see bulged can in photo).. If Im using my multimeter correct I only see one of the three caps accepting a charge. ... I dont know how this thing functioned. (EDIT: two caps accept a charge.. not sure which is the dead one) EDIT: one of the 40MFD caps was blown.

I installed two 47MFD caps in #1 and #2 position, then 50MFD in 3,4 position...

Hum still there but when the volume is turned WAY up noticeable less "noise"...


Who knows whats blown up upstream... the fun continues... time to clean up for now..

 

[jaymanaa]

Yes, I've decided to just do it and be done with it Solder iron heating now..

I'm a little concerned about the orange drops I bought now.. they are 600v and quite large.. especially the .25MFD replacements... I had planned on replacing the .02MFD caps on the last stage of the tape section with the .22MFD orange drops (again this is something I read DC suggest to bring the bass up) to eliminate the use of the loudness switch... They are pretty gi-normous caps..

Thoughts? are there orange drops with less V? I bought all my parts from a place calaled tubedepot (tubedepot.com)... very reasonable prices compared to mouser...

They do make them in a 400v "size" which is way smaller, and Antique Electronic Supply carries them. Probably a buck or two each. FWIW, I'm remembering more about the first time I built mine, and it seems like the 3hy choke (40 - 50 DCR) really made things quiet, and the voltages fell nicely into range as well. Ripple may not be the source of your hum though. Set your digital meter on AC volts and check your B+ to see how much AC is riding on it. Some say 3v is ok, but I prefer a decimal point before the first number.

 

[barchetta]

Today I decided to upgrade the .02mfd capacitors on the output of the tape section. I carefully desoldered the vintage ceramic caps and saved them. I had previously needed to use the modified loudness switch when using tape output or I had little to no bass. I decided to go with the same values that are on the output of the "preamp" section, .25MFD.. I used two orange drop caps. The result was no need to dial in the loudness switch.. and as far as I can tell it completely removed hum... there is some noise when the volume is cranked to about 3/4.. but I dont expect to use it there too much...

However, the bass is slightly less punchy than it was.. so Im going to play with these values.. I have a couple of .1MFD orange drops Im going to solder in..

Id like to note something I have discovered... when using the loudness switch, the .025 caps that are switched in APPEAR to be slowly removed from the signal as you increase the volume.. which is exactly how you'd think a loudness switch would work... I've NEVER had one operate like that but it makes sense.. however, for my purpose I do not like it..

I'll keep updating... although I dont know who is listening..

Oh and just for interest I connected my Onix 88 CD player direct to my Pass Labs Aleph 3 amp.. I was curious... the highs were incredible... mids.. not so much.. and I felt like I was listening to a solid state amplifier.. (fwiw, the volume was on the high side so plenty of gain from my CD player..)

So.. I'll keep playing with this little gem of a preamp... Id like to get those highs back if possible but am not going to count on it.

 

[barchetta]

They do make them in a 400v "size" which is way smaller, and Antique Electronic Supply carries them. Probably a buck or two each. FWIW, I'm remembering more about the first time I built mine, and it seems like the 3hy choke (40 - 50 DCR) really made things quiet, and the voltages fell nicely into range as well. Ripple may not be the source of your hum though. Set your digital meter on AC volts and check your B+ to see how much AC is riding on it. Some say 3v is ok, but I prefer a decimal point before the first number.

this is really going to show my lack of knowledge but I dont know where or what B+ is.

 

[GloBug]

B+ is the high voltage on those caps you were checking. (Carry-over from when batteries were used. Also known as HT or high tension.)

B+ starts at the rectifier, it is high voltage DC current. Anything before the rectifier is high voltage AC.

The rectifier is usually a tube,(sometimes small diodes) and is the first single tube connected to your power transformer.

 

[jaymanaa]

B+ is the high voltage on those caps you were checking. (Carry-over from when batteries were used. Also known as HT or high tension.)

B+ starts at the rectifier, it is high voltage DC current. Anything before the rectifier is high voltage AC.

The rectifier is usually a tube,(sometimes small diodes) and is the first single tube connected to your power transformer.

Yes, the B+ is the voltage that will make you throw your shoulder out when you jerk back from accidentally touching it. It can also give you a rusty zipper.

 

[barchetta]

I'll start checking voltages.... however its very bad when one inadvertently bends a resistor so it touches another connection on a tube socket Gives you scratch your head HUMMmmmm luckily it didnt seem to cause damage.

I think all caps are in place now in regards to the power supply and the tape out section... I dont think any on the selector switch effect tape? Maybe Im wrong.. I'll look closer.. I've listened so many times inbetween changing caps I dont know if I've done any good.. other than less hum.. it really does sound sweet though.. Im using remastered steely dan as my test material.. Cymbols are pretty airy considering the quality of my speakers ($1000, 2 way monitors)..

Bass is a little tighter with .1 MFD caps on the tape section outputs.. But Im still not happy.. Im also using 600v caps.. Im gonna order some 400v orange drops in some different values.


I did adjust the hum pot so I had 6.3 volts at the filaments.. it was way way low. Im letting it warm up now


I still have hum however.. Its hard to hear with ambient noise but its there and if I put my hand on a woofer I feel it.. My guess is this would be where Id have to go with DC on the filaments? With the phono section removed, could I do it with the stock transformer? Just install a solid state rectifier? Or use the rectifier tube and step it down with a large resistor? Im getting out of my league here of course...

 

[jaymanaa]

I'll start checking voltages.... however its very bad when one inadvertently bends a resistor so it touches another connection on a tube socket Gives you scratch your head HUMMmmmm luckily it didnt seem to cause damage.

I think all caps are in place now in regards to the power supply and the tape out section... I dont think any on the selector switch effect tape? Maybe Im wrong.. I'll look closer.. I've listened so many times inbetween changing caps I dont know if I've done any good.. other than less hum.. it really does sound sweet though.. Im using remastered steely dan as my test material.. Cymbols are pretty airy considering the quality of my speakers ($1000, 2 way monitors)..

Bass is a little tighter with .1 MFD caps on the tape section outputs.. But Im still not happy.. Im also using 600v caps.. Im gonna order some 400v orange drops in some different values.


I did adjust the hum pot so I had 6.3 volts at the filaments.. it was way way low. Im letting it warm up now


I still have hum however.. Its hard to hear with ambient noise but its there and if I put my hand on a woofer I feel it.. My guess is this would be where Id have to go with DC on the filaments? With the phono section removed, could I do it with the stock transformer? Just install a solid state rectifier? Or use the rectifier tube and step it down with a large resistor? Im getting out of my league here of course...

I used the stock transformer 6.3 windings with a small full bridge rectifier and a large cap (maybe 4700x16v). Some say Eico iron is specd pretty tight, and the DC conversion will add some current draw, but mine has logged enough hours that I no longer worry about it. You may have to adjust the uf rating on the filament filter cap to zero in on the 6.3 exactly. Larger uf rating, v will go up, smaller, voltage will go down. Something like this will do the trick for the rectifier, but it's a whole 99 cents. GBU4J Fairchild Semiconductor Bridge Rectifiers

 

[jaymanaa]

I just popped mine open and it was a 4700uf that I used. Did you ever measure the AC voltage on your B+? Just set your digital meter to AC and put one probe on the chassis ground and one on the positive of your first filter cap. You want a low low number there.

 

[barchetta]

B+ is 315v AC on PIN 1

And I see 375v DC on the two DC pins 6,7 of the rectifier. I see 31MV of AC in those pins.

I've done all the caps in the signal path and bypassed the selector switch..

I still have some hum.. can feel it when I touch the woofers.. Im using a small class A amp.. once I fix whatever is wrong with my 100w class A Im gonna hear it Im sure.. and Im sure its "normal" with the AC going to the tube heaters...

Im also a little let down with the orange drops.. its a bit harsh.. perhaps some break in.. I'll let it run for a few days..

Voltages ok?

My outlets are running @ abt. 122v AC..

 

[jaymanaa]

Ripple voltage sounds great, I think youu are dead on about it being time for some dc heat. I don't mind a few orange drops here and there, but Hovlands, Auricaps, and Kimbers can be much better for coupling stages etc.. But like you say, give them some burn in time before you make up your mind.

B+ is 315v AC on PIN 1

And I see 375v DC on the two DC pins 6,7 of the rectifier. I see 31MV of AC in those pins.

I've done all the caps in the signal path and bypassed the selector switch..

I still have some hum.. can feel it when I touch the woofers.. Im using a small class A amp.. once I fix whatever is wrong with my 100w class A Im gonna hear it Im sure.. and Im sure its "normal" with the AC going to the tube heaters...

Im also a little let down with the orange drops.. its a bit harsh.. perhaps some break in.. I'll let it run for a few days..

Voltages ok?

My outlets are running @ abt. 122v AC..

 

[barchetta]

Thanks.. I'll burn it in and order some boutique caps if I don't like it.. And at some point.. with some assistance here I hope, convert the heaters to DC.. thanks all for your help..

 

[barchetta]

Guys.. I have let this thing burn in and Im not happy.. I wish my old caps were back in.. however.. Im noticing now a problem which might explain some things.. my preamp started to fade in and out of what appears to be bass level... of course when you add bass you feel warmth.. which might explain why I feel like this thing sounds solid state now..

Just moments ago I turned it on and within 10 minutes bass faded into the signal.. very strong bass.. or perhaps volume.. but I think bass.. the other day it actually faded in and OUT a few times..

Since all the caps are replaced but the tone caps and Im using the tone circuit right now, I guess thats where the problem might be?

Or maybe the tubes? I will put the two I took out of the phono section in and see what happens..


Sorta talking out loud here but curious as to what in theory would cause this fade in and out situation.. Im off course assuming its the preamp and not my Aleph 3 power amp or the CD player.. think its pretty safe to say its the preamp..


regards...