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I'm working on a McIntosh MC60 (model with the neon bulbs for voltage regulation) that is putting out a short, low pulse every 4-5 seconds. It has been completely rebuilt and worked great until one of these events caused it to start pulsing (not sure which): Event One- One of the 5U4 tubes...

I have a chance to buy a quad of good used Realistic 7591A tubes at an okay price, but I know nothing about the Realistic brand of 7591s. I know Radio Shack did not make their own tubes, but I don't know who made their 7591s or if they are any good. The guy selling them said the construction...

I have a pair of JBL L110 speakers utilizing 033 tweeters. Both have recently rebuilt crossovers. Recently I noticed that one speaker had less treble than the other and could not be brought up to the other's level with the tweeter crossover control. Note: I ruled out amp or source material...

I need to get several LPs that do not have the RIAA equalization for testing of old hifi systems that do not have RIAA equalization circuitry. Today I saw some old Dean Martin, Frank Sinatra and Doris Day LPs at a swap meet that appear to be from the 1950s. The Dean Martin and Doris Day...

I rebuilt my Eico ST-84 preamp which consisted of replacing all coupling and bypass caps, rebuilding the power supply and modifying the loudness control using the recommendations found here on Audiokarma to make it the conventional circuit. I like to use the loudness control function, but the...

I have a Collaro Conquest turntable that sort of works. It's inconsistent because is sometimes doesn't drop the record and usually drags the stylus across the last few grooves of the record at the beginning of the change cycle. It's been throughly cleaned and the idler wheels have been replaced...

I bought a Marantz 8b several months ago and it works fine, except that it is a little lacking on the lower end compared to numerous other amps I own and have worked on. It has the original Goodall caps in the 6BH6 section, but the coupling caps to the output tubes are Sprague 160P black caps...

I am considering buying a Marantz 8B. However, I have a choice between two different units with significant differences. The first is electronically original (except for replacement of the selenium rectifier and two bypass capacitors) and includes tube adapters to allow use of 6AU6s in place of...

I am refurbishing an H-K Citation II and found that the bias/balance meter has a burned/open internal series resistor. Surprisingly, the meter movement is fine. However, the resistor is burned beyond being able to determine its value and I can't find any sources that list its value Does anyone...

I refurbished a formerly non-working Fisher 400C preamp for a customer and I found the balance control does not completely silence the other channel when turned fully CW or CCW. The schematic shows that the non-signal side of the balance pots go through 8.2k resistors to ground (R40 and R72)...

I have a question about the modifications provided in the Dynakit Mark II manual that will allow it to be used to power an external preamp that needs a power supply like the Heathkit WA-P2 (the preamp would plug into the octal socket in the side of the Mark II). One of the modification steps...

I previously posted a thread asking about winding inductors to rebuild two JBL N2600 crossovers that had essentially been gutted in the past. (Thanks to everyone for their insightful guidance) Now I have an issue with the schematic vs what little wiring still exits. Although the capacitors and...

Normally I would never consider winding crossover inductors, but someone wants me to build them two JBL N2600 crossovers almost from scratch. Someone had gutted the original crossovers and left only the box, switches and pots. Fortunately, it's a relatively simple crossover with few components...

I need to thin my stack of turntables and want to put the least desirable cartridges in the ones I'm parting with (cartridge swap). However, I'm not too familiar with how each cartridge compare against the others and I'm hoping someone can help me rank them. In addition, I have an unmarked one...

I have a McIntosh C20 that has significant crosstalk/signal bleed among the various high power inputs on both channels. When the input selector is set on the input with the signal, it sounds great and can be controlled by the volume and balance control. However, when you switch it to the other...

I am preparing to refurbish a McIntosh C32 (new ribbon cables, caps and upgraded ICs). In searching various posts, I have been able to determine most, but not all, of the common equivalent part numbers for the McIntosh ICs in the unit. I'm hoping someone has a cross reference or experience in...

I'm hoping someone can enlighten me regarding too much bass coming out of the optical output of my Visio TV. I'm using the TV as the HDMI switch for all of my devices (cable box, Roku, FireTV, etc.). I then connect the optical output from the TV to a DAC and then to my McIntosh C32 preamp. The...

I'm hoping someone can get me the correct information regarding whether black plate 6L6GCs by any manufacturer (but especially RCA) can cause red plating in Mac amps (no other cause other than the tube having a black plate)? The friend who told me this said that there is no explanation for it...

I came into possession of a classic McIntosh MC275 that still had all of the original capacitors and sounded kind of tired, so I refurbished it by rebuilding the power supply and changing out all of the capacitors with audio-grade polypropylene ones. It sounded good, but not as good as I had...

I have a question that I'm hoping the veteran tube amp builders/refurbishers can answer. I've read in a number of places that you can enhance the sonic quality of a tube amp or preamp by increasing the value of the coupling capacitors because the manufacturers in the past used lower values as a...

I have a chance to get either an Eico ST-70 or a Fisher KX-200 integrated amp. Both are working and in good shape. The Fisher is about double the price of the Eico. The seller (a friend) said the build quality of Eico is as good or better than the Fisher (I haven't seen them yet). If I get the...

I am repairing a friend's original issue MC275 that has distortion in the right channel, and I sensed a little distortion on the left channel, but not much. Upon looking at the components I found that someone had rebuilt it, but used incorrect values for the coupling caps (all lower values than...

I finished restoring a Heathkit SP-2 preamp and it sounds great on Aux, but just okay on phono. Has anyone rebuilt the phono module and improved the performance? I rebuilt the tone and loudness modules and both brought noticeable improvements. I could use the Heath schematic and build a new...

I'm in the process of restoring a Mcintosh C11 and a previous owner did a very poor job rewiring/changing the power supply section. I am trying to bring it back to the original circuit (with new rectifiers and caps). However, because of their rewiring, I only have the schematics to go by. I...

I won a working McIntosh C11 in good shape on eBay for a decent price. However, when it arrived today, I found the seller's packing was lacking, and it now has a broken faceplate. I'm going to put in for an insurance claim, but I need to find a source of a replacement faceplate in order to...