Tom Mobley Posted September 23, 2002 Share Posted September 23, 2002 At AES they have the Auricaps in either .22uf @ 450V or .33uf @ 450V. which of these would be better in the HF-81 ? Original is .25uf 2 200V. I believe these are in the phono pre-amp section, attached to the 12Ax7's on the left of the chassis. How does this work? there's four 12AX7's, looks like two of them are the phono pre-amp and the others are tied in with the 12AU7's. Is there separate pre-amps for the phono and then the AUX, tape and tuner? I've got the 40uf Sprague Atoms, a nice NOS pair of Sylvania 6CA4/EZ81's for the rectifiers, a nice matched quad of of NOS Ratheons EL84's all coming in this week. I need to order the rest of the caps now if this stuff is going to be available during my next string of off days. I'm ordering the four .1 @ 400V Auricaps from AES, I'd like to get the .22 or .33 in with that order. Any help appreciated here. Tom This message has been edited by Tom Mobley on 09-23-2002 at 11:07 PM Quote Link to comment Share on other sites More sharing options...
prodj101 Posted September 23, 2002 Share Posted September 23, 2002 that should work. Lol, I'm using some 400 uf capacitors in my home made tube amps, talk about a stiff power supply. ------------------ New music system: 2.1 using SF-2's (soon to be RF-7's), and an RSW-15. for amplification Mcintosh MC02105, B&K PT-3 preamp, Sony SACD player. pioneer turntable. Computer uses Promedia 2.1's. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted September 24, 2002 Share Posted September 24, 2002 Tom, have you looked carefully at this page? http://home.earthlink.net/~eico_hf81/eico_hf81_wiring.htm I do believe the stock couplings caps are .025 with Stevens going with .047. I recommend going with .027 or .033 which I believe is only available in the 600v version. Here is the full list of available Auricaps: http://www.audience-av.com/auricap5.htm . I only think AES carries the .047 (I wouldnt go below .025). This is the easiest to find size. Looks like AES does have good prices compared to other dealers. It will get a bit pricey replacing all the caps as they number 10 or so total. You need to do the linestage/output coupling caps definitely, and the phono if you plan on using it (You have the phono, line stage, and output coupling caps). Let me check my schematic with parts list once again for all this. kh Quote Link to comment Share on other sites More sharing options...
NOSValves Posted September 24, 2002 Share Posted September 24, 2002 Tom, You are correct the Phono section does take .25 MFD @ 200V. The coupling caps to the output stage take .025 but I personally would up that value to double I'm not familiar with what aurocap offers. There are also some .1 MFD's to be replaced also. If you want me to get my unit out its bone stock and go over the schematic and make you a complete parts list of the stock values I will but can't do it until tonight after work. I'll be doing it anyway for mine. I will first use mine in its stock form first though. Craig ------------------ HH Scott 299 Amp HH Scott LT-110B Tuner HH Scott P-87 Turn Table JVC JL-F50 Turn Table Sony CDP-CA7ES CD Drive 1985 Walnut Heresey I W/Layne Audio Woofers KSW-15 Subs>c> Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted September 24, 2002 Share Posted September 24, 2002 It used to be widely considered to increase the coupling caps value to lower the bass rolloff. Lately, with communicating with various DIY guys, there is a movement away from this practice and I tend to agree. While I would not go below the value, I would not above .047 for the coulpling caps either; Gary Kaufman, who has redone many vintage units inlcuding EICOs/Scotts/Dynaco agrees on this as does a host of other DIY guys. And frankly, I have not preferred the sound with much higher coupling values. The bass via the EICO is already very good, even with stock values. Raising the coupling value too much can take away some of the bass refinement and lead to instability. I actually LOWERED my coupling value on my Moondogs just a bit and PREFER the sonics, but I would not recommend this with the EICO. Higher values means more cap in the path while too low and your bass begins to suffer. I tend to think the EICO has a great balance as it is, although bumping them up a bit is fine. I prefer Jensen Copper oil caps in my SET amps and have been thinking of giving some oils a try in one of the EICOs, thjought not of the Jensen variety due to cost and size. kh Phono Linn Sondek LP-12 Valhalla / Linn Basic Plus / Sumiko Blue Point CD Player Rega Planet Preamp Cary Audio SLP-70 w/Phono Modified Amplifier Welborne Labs 2A3 Moondog Monoblocks Cable DIYCable Superlative / Twisted Cross Connect Speaker 1977 Klipsch Cornwall I w/Alnico & Type B Crossover Links system one online / alternate components / Asylum Listing f>s> This message has been edited by mobile homeless on 09-24-2002 at 08:18 AM Quote Link to comment Share on other sites More sharing options...
Pland Posted September 24, 2002 Share Posted September 24, 2002 Hi, Stay within 10% uf of the original ceramic cap values(coupling caps)and you'll retain the overall voicing of the amp.Voltage is not as big an issue,as long as you increase the capacity.This is of course assuming you want restore the amp as close as possible to it's original sound.If I recall,in an HF 81 you have two paper Sprague under chassis electrolytics,one above chassis can electrolytic,and four ceramic disc .025 coupling caps.I'd start here with stock uf(auricap gets close)for the ceramics replacement,higher voltage if that's all that's available.The electrolytic paper caps can be replaced with Xichon,Panasonic,etc.,whatever fits.Normally ,the Sprague above chassis can is OK,but use a Variac to initalize and reform all caps before using the amp after the rebuild. At all chassis grounding points,clean the chassis with a Dremel tool with the wire attachment,and re-attach all grounds.Spray with De-oxit. Check the Bias resistors and replace if they've drifted over 10%. Clean all pots,and controls(I like WD40)and lube with De-Oxit. If you get lucky ,the above will yield a real quiet HF 81 with tranny's that don't glow from heat.Check voltages to insure all values(available in the build manual). Best, Pat Quote Link to comment Share on other sites More sharing options...
NOSValves Posted September 24, 2002 Share Posted September 24, 2002 Pland, Great advise there. You have good luck using WD-40 on the Pots hmmmm. So I take it spray and work them with the WD-40 let them drain and then again with DeoXit. I bet that could bring in those old pesky ones that are real corroded Huh ! I'll have to try these onb the next one I do that had volume pot tracking problems. The last 2 Scotts worked great must of been used lightly and kept in dry storage. Some of those pots can be real bad Craig Quote Link to comment Share on other sites More sharing options...
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