[morzh]

As I remember it, the shock from that B+, about 250VDC, felt worse than the shocks I experienced from 220VAC.

[TV MAN]

Oh the adventures we had a young ones! That Zenith was given to me with a shrunken and bloomed picture, but found if I set it on it's side and bumped things around, it would sometimes kick in and play like it should. I knew it was around the horizontal and HV section, so unwittingly I started tapping around the 6HV5 regulator pins with what I had on hand, an pencil! I figured it was a loose connection. So, yeah, zapped It actually turned out to be a bad tube, saw the cathode lead spark while thumping around the the picture would straighten out then get bad again. I wasn't even driving age but loved those old tube Zeniths, and this one was almost like new at the time. Still have it! Just never had the heart to get rid of it. I used it until I moved off to college after a Westinghouse re-tube. The worst I had was a shock from the focus voltage on a SS TV when my necklace (yeah, I was a young punk) hit the PCB on the neck of a TV I was working on. Yah! No more necklaces

Added: This "crystal generation" we have now will never know the thrills and adventures we X'ers and Boomers had growing up! Their biggest adventures circle around a touch screen and keyboard! They'll never experience shocks, skinned knees, cut/burned hands and the thrill of putting something together from scrap parts from a hand sketched paper with unreadable hieroglyphics copied from a magazine or radio book and making something work! They really don't know what they are missing!

[morzh]

Well, should I say that the electrical stuff was the safest of what I did otherwise as childhood entertainment.
But...All of us survived, even the guy who ate the content of the champagne bottle, stuffed with a healthy dose of calcium carbide, then with our combined urine samples in lieu of water and corked with a champagne cork, reinforced with many layers of black tape.
He was the most curious of all and was wondering why the bottle would not go (a champagne bottle can withstand pressure many times that a regular bottle could ), and he decided to help it blow.
Oh the childhood in a Russian village...well, we did not have an Opera house. We had to entertain ourselves.

[MrFixr55]

@TV Man and Morzh, LOL!!!  "We did not an Opera house. We had to entertain ourselves."   What is it with us guys and making things blow up (either accidentally or on purpose)???  Sounds like we all kept our Guardian Angels busy!  Yes, the snowflakes may be able to code (If they are not rotting out their brains playing Doom or Grand Theft Auto), but you guys are so right!! the thrill of victory resurrecting a dead antique radio, car, etc, or even recycling / saving money by fixing one's dead washer / dryer / refrig / dishwasher, pool filter, lawnmower, chainsaw, even flat panel TV, etc., and saving megabux in the process!

[TV MAN]

Alright, now jumping back on the subject of building an amp. I am going to reorder some resistors to get something that might not smoke if I look at it wrong. I've been doing quite a bit of planning and researching on design, layouts, and common mistakes (yes, I'm guilty). One thing I have noted is that I often have hum and buzz problems, and on one of my previous posts I had someone mention ground loops. I've usually been able to get the problems resolved - for the most part. One mistake I am probably making is using the stainless chassis as my chassis ground. I am considering having my chassis float (to some degree), and use a heavy (#16) copper wire to tie my grounds directly to the B-. Then, ground the chassis through a safety cap and 100ohm resistor, tied from B- to chassis, then ground pin on the power plug. I've been reading in DIY Audio Projects.com and there's quite a few tips that I am taking notes of. So, with various grounding points on the SS chassis, that could be giving me hum problems. I also read something about bucking caps on the filaments. I'm sure I can get this together and running in a few hours, but I am spending quite a bit of time planning, drawing and researching. I'll also take notes while I am working so hopefully the 2nd and future projects will go smoother, and save some trouble shooting.

So, since this is an experiment, I will be trying some different OP trannys and tubes. I initially want to get it working then start playing. I found a set of New Sensor trannys that bolt up and match the holes already in the chassis exc. for 1. That's my 1st try. I have a new set from Musical Power Supplies, but am trying to decide if I should try or return. They don't match many holes and I originally thought they were UL (ultra linear), but they have 2 sets of primaries for different tubes. 8k and 6.6k. I saw a set of UL HiFi trannys but more money ... trying to make this budget friendly, yet still sound good. The trannys I have are "basic", not HiFi, good for up to 25w. Although I really doubt I could hear much difference.  

One thing has me kinda scratching my head is the power trans. It is physically smaller than one I used previously on a PP kit. According to the label, it is .2 (200 ma?) on the 230v, same as the others, which should be adequate. The basic circuit schematic I'm following specs 160ma. It does only have 1 filament winding (3a) whereas the others had 2 or 3, so this could be part of the size difference. So I guess the current meter is the best way to know where I am.

[morzh]

Tim

Unless your GND is B-, I am not sure they need to be tied together.
Nothing's wrong with it either.
But I would make chassis GND.
You could make the electric GND a thick copper wire, but I would make sure the chassis is tied to it.

[TV MAN]

Thanks Mike. I'm reading in AK and some other threads. I don't want to overthink and complicate things. Trying to keep it simple, yet work good. I'm open to any advice.

[morzh]

https://schematicsforfree.com/files/Audi...Manual.pdf

This is Eico HF-22 schematic. One of the best output amps out there.
I own a couple, restored a few years ago. They sound great. No hum or anything.
It is an ultralinear topology.

As you can see, they do have B- at the GND, and it is not isolated from the chassis. The RCA inputs are bolted to it.

This is Mac, MC275. Same story. This is the original.
https://rubli.net/classic_amps/files/amp...ircuit.jpg

[radiorich]

Hello mike,
yes , I have been wanting to build a amp for some time I do have a smaller amp that I built years ago .

Sincerely Richard

[TV MAN]

I've done some reading and I don't know that I am any wiser I've also been studying the pictures of the chifi kits assembled and I have noted several things. One things I've noted is that it looks like they are tidying up things present day over their builds several years ago. I see them using terminal strips rather than open air like before. I really only see anything special on their preamps, like a ground bus, which those are a lot more sensitive. It looks like the power amps use the chassis. One possible mistake I've probably made is tying the B- to chassis ground right on a transformer bolt. That may not be a good choice. They talk about stars, but I don't know if they are talking about those connectors with the teeth or if it's running the grounds to a common point. Another mistake I could possibly have made is tying the grounds to different points in a single stage rather than all to the exact same point. I've also grounded the input jack at the level control rather than the jack. They mention tying the jack to chassis ground rather than at the control. Anyway, maybe I'm overthinking things again. I've reordered my resistors, the itty-bitty ones anyway, and some decent coupling caps.  Rich, maybe you can learn from my mistakes so hopefully your amp build will go more smoothly.

On a different subject, I was listening to my last kit amp and things were sounding awful. I really thought it was my speakers or amp clipping. One speaker sounded really bassy and bumpy, the other had no bass. I began switching R&L inputs, playing with the balance, and it followed the inputs. I determined it was not in the speakers or amp. It's the preamp messing up. It just sounds flat, like it has no depth, lackluster. Sooo, I pulled the cover and looked things over. It's a Dyna Pat 4, and I had changed the Q4 driver output (due to noise/static) with the Darlington kit from "Upgrade my Dynaco". I really couldn't remember doing that but it's my work. I also replaced the output coupler cap. None of the others, so I suspect the others have died. It happened gradually, so I really didn't notice until it got so bad. It's on the driver board because it doesn't matter what input I use. Just sounds ... uh, yah, blah.

[TV MAN]

Mike, that Eico has a very unique output tranny. It looks like 2 primaries in series, I had read about a design similar to that, Pearl I think, from the early 1950's, where they had the 2 output tubes in series. It was interesting. The Eico looks pretty straight forward beyond that.

[morzh]

>>I've done some reading and I don't know that I am any wiser

Ecclesiastes 1:18. 

- For much wisdom can result in much sorrow, and those who increase their knowledge also increase their grief.




As for the HF22, it is an ultralinear amp.

[MrFixr55]

I think that the Heathkit "Williamson" amps, popular in the mid to late 50s had "ultra-linear" output transformers with separate primaries like this, which were tied together at the B+ lead. I need to rebuid these but I have a WA-P5 (bad output tranny, 2 WA-P4s (one looks like a good homebrew) and a WA-P3. I believe that between these, I have 2 good Acrosound TO300 output transformers.

Other than the phase invertor circuit, the Eico seems very straightforward. Interesting that it uses cathode bias as most HiFi high powered amps use fixed bias. Interesting also that they allow a choice between 6L6 and EL34s. Seems that if they jumpered pins 1 and 8, they would be an even swap (assuming pentode operation and that the bias voltage is similar between the 2 tubes.

The Mac is a total monster, what with pro 70V line outputs for PA work, the KT88s / 6550s in the output stage, etc. Same type of phase invertor as the Eico, but I don't get the setup for the 70V line. I can't see the same amount of power being delivered by the 70V circuit as is available from the output transformer.

Generally speaking, in building a HiFi amp, a ground "mecca" is a good idea. this is often done with a piece of wire much bigger in diameter than needed for the B return for all loads. The "mecca" is grounded to the chassis at only one point. I believe that this nis at the input jacks. I have a 1947 Philharmonic AM radio and 78 RPM changer, an AA5 radio where they actually did this.

[TV MAN]

Well if memory serves me right, I think I build the single ended amp using chassis ground. I had hum issues but found I neglected the filament ground and had a tube messing up. After I got that sorted out, it was quiet. The PP amp built last had hum issues to this day. It used a pcb , very little point to point.

[MrFixr55]

What may be lacking in the PP Tube amps may be the 2nd harmonics, which some, especially RCA back in the day called "euphonic". (Of course if an amp had <5% distortion, RCA called it "distortion free".) I am not sure, but I thought I heard some pipe organ builder state that 2nd harmonics are pleasing. I have 2 815s and want to build a dual P-P amp with those. I had a good ear as a kid and can sing mostly on key (not with a good voice but at least on key), but I can't hear the whine of a flyback or the ticking of a watch anymore. Not from rock or heavy metal (both of which I despise), but from being around too many machines, engines, etc. without ear protection. Standing 3 feet in front of our church's 62 rank pipe organ (<3000 pipes) with the choir may not be great for my ears, but I absolutely love it!