Magnavox 6V6 PP - 175 vs 8802, comments?

volcano_pioneer

New Member
Recently I have acquired a Magnavox 175-67 and an 8802 (both are 6V6 PP). Replaced coupling caps in both, added power switch, pilot light, speaker binding posts, 3 pair of input jacks, input rotary selector switch, volume pot, wood trim. Now I'm wondering what are pros/cons of these two models. I have not yet had opportunity to do A/B comparison with same speaker pair. The 175 has noticeably larger power transformer and maybe slightly bigger output trans - will that mean more output "headroom"? The smaller size and lighter weight of the 8802 are attractive for a bedroom system. I'd appreciate any comparison comments from those of you who know these units. Thanks for your help. (I've attached pics of the 8802, but don't have a picture yet of the 175. The 175 looks basically the same.)
 

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Yes the 175 should deliver more power. 6V6s are biased at 40 mA each vs. 25 mA in the 8802. On the other hand, 6V6s should last a LONG time in the 8802.
 
The larger OPTs may also go a little deeper in the low freq. range. Also the 175 has a choke in the PS, while IIRC, the 8802 does not. Should make for a quieter PS....
 
I have a 175 and was thinking about a 8802 because of the slightly smaller foot print. I was thinking of using it in a bi-amped system but if the low end suffers I'll probably get another 175. :scratch2:
 
Most 175-67 amplifiers I have run across, use the larger power transformer because they usually run a preamp/tuner. My 175-67 came out of a TV/radio combo.
 
Cademan, I believe you are correct. There were additional power transformer connections to the large molex plug on the 175 that were not present in the 8802. The 175 also had a connection labeled "external speaker" that was driven from the smaller molex plug for the main speakers. I haven't compared them side by side, but it does seem that the 175 has more output "power" than the 8802 when I'm driving the not particularly efficient speakers at my work bench. I've listened to the 8802 in a bedroom system with relatively efficient speakers and it has plenty of power for them and seems to go low enough. I'll try them both with Dynaco A-25s (about 88db, I think) and see what differences I can discern. Waiting to apply and dry the final coat of lacquer on the 175 wood trim.
 
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I would be interested in your impressions of the low end for both. I'm still on the fence about using a tube or SS amp for the low freq.
 
The 8802 uses the smaller 6CA4 rectifier tube...and doesn't have a choke in the power supply like the 175. The PT in the 8802 is smaller also... So overall...I'd say the Power Supply is beefer and better on the 175. I also like the look of the bigger 5AU4GB rectifier tube on the 175 also.

As to any circuit difference...I don't understand enough to make any comment.

True the 8802 chassis is more compact....but the 175 is nice also.

I like the fact that the 175 is older....I believe 1958 vintage...and I believe the 8802 is newer...perhaps by a few years. That is added cool factor in my book.

Plus the 175 has more real estate on the chassis around the OutPut Transformers...if you want to upgrade these down the road at anytime...I think this is a great feature as a project down the road. One could add OPTs that have 4,8 and 16 ohm taps if so desired. This would expand the "utility" of the amp markedly, IMO. I do like the sound of the 175...as is. It is great.

I do have both a 175 and a 8802. I use the 175 everyday...but have not got the 8802 up and running yet.

:music:
 
The output transformers are very close to the same, but the power transformer is definitely NOT the same!

One thing that will work with the 88xx amps, is to remove the 6CA4 rectifier tube, replace it with a solid-state diode rectifier (pair of UF4007 or such), and add a choke (1H 55 ohms, 200ma, is good enough- in fact, the replacement choke for the Dynaco ST70/Mk III is perfect- 1.5H, 200 ma). Wire it with the diodes first, then a 40uf cap before the choke, and a 100uf cap after the choke, and take output tube power from the output of the choke. That will bump B+ up to about what an AMP175 has- and with much better regulation and filtering (cleaner power) too. The amp will make more power, and the bass will be better too.

The reason you can get away with this greater voltage and current from the B+ winding (about another 8 watts of draw), is that you're getting rid of the heater current the 6CA4 is now drawing (about 6.3 watts) from the same transformer. Yes, the net draw is a little higher, but not enough to cause significant heating of the power transformer (especially since a stand-alone amp isn't powering the tuner or preamp, either)...

Regards,
Gordon.
 
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I would be interested in your impressions of the low end for both. I'm still on the fence about using a tube or SS amp for the low freq.

I've never had an issue with lack of bass on a tube amp. I know the whole thing about supposedly needing gigantic output transformers to get to 20hz or whatever, but I have never ever had an issue with console amps and lower-powered receivers/amps getting nice and deep.
 
175 can pack a punch

the 175 has plenty of power to spare when set to stand alone running 5u4g. without the tuner and preamp which this unit provides power for as well you can upgrade to 6L6 power tubes keep the original output transformers and squeeze out about an additional 3 to 6 watts of output per channel. the unit could easily be upgraded with higher output transformers and either a second rectifier added or switching to solid state rectifier. this is the 175ff that I converted to stand alone its running Russian 6P3S power tubes and a 6sn7 was added as the input stage
 

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Taper240 - convert to 6L6? That is VERY interesting to me. I'm a fan of 6L6, one of the better sounding tubes to my ear. (Once had a Dared SE 6L6 amp and was very pleased with it.) Are pin-outs the same as 6V6, or some adjustments required? Plug and play would be fantastic. I'll appreciate any detail info you can give me. Thanks. Here's a pic of the 175 I just did.
 

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I would be interested in your impressions of the low end for both. I'm still on the fence about using a tube or SS amp for the low freq.
I've used both a 175 and a Dyna ST70 on top with an Audiosource Amp3 for the bass driving modded Speakerlab K's. Either sounds great. Bass goes a little lower and is cleaner using ss. JOHN
 
convert to 6L6? That is VERY interesting to me. I'm a fan of 6L6, one of the better sounding tubes to my ear.

Hi, the 6L6 has the same pinout as the 6V6. You can use a 6L6(GC) in place of a 6V6 but not the other way around. Also, take into consideration that the 6L6 has a higher heater amperage rating so the amp, specifically the power transformer, needs to be able to supply the current without overloading the power transformer.

Adding a 6L6 to the 175 won't give you any more power unless you can supply them with more B+. It's something you can't really do without modifying the circuit or having a different power transformer that can supply the rated voltage.

I use the 6L6GC in my AMP176-67 but I modified it to squeeze out about 20-25 watts per channel. My amp no longer resembles a stock 175. I added a bigger power transformer, removed the 5U4 and put in solid state diodes, plus I swapped out the output transformers for bigger one's.

I believe member GordonW has done many mods to these amps with awesome success.

These are great amps to experiment on. :thmbsp:
 
The larger AMP132/AMP142/AMP150 (there are three sizes, believe it or not) power transformers, when converted to solid state rectification, can handle running a quad or 6L6s (PP 6L6). Some of the earlier AMP175s also have the large power transformer (the lamination stack is close to 1.75" tall, as opposed to just over 1.125" or so for the smaller ones).

The AMP132/AMP142/AMP150 low-section output transformers (black bells) can handle a pair of 6L6s each, too, and give about 20w/ch of VERY good sounding audio.

OTOH, the stock AMP175/88xx series output transformers are pretty much tapped out at 12-14 watts max. No matter how much B+ you throw at them, they will start to saturate at above about 12 watts full-range...

Regards,
Gordon.
 
You also run into impedance mismatching when trying to run a 6L6 on the 6V6 output transformers. The Magnavox transformers should be right about a 10k primary and a 4 ohm secondary. A 6L6 would want about half that impedance on the primary. Factor in the power limits and such of the output transformers, and you're better off with keeping the 6V6, or maybe changing it to a 6BQ5 that would end up at pretty similar output power levels.


The larger Magnavox transformers worked because they are push-pull-parallel, running 4 6v6 tubes on each channel. It works out to about a 5k primary vs the 10k that a pair of tubes will work into.
 
Yep- I measured about 4.5K into 4 ohms, and 9K or so into 8 ohms, for the 300-024 PPP output transformers (AMP132, etc). That works fine with 6L6s.

Regards,
Gordon.
 
I recapped my 8802 and stuck with the original PS and OPTs but opted to beef up the coupling caps. Bass response is wonderful on my Klipsch Quartets!
 
In browsing through AK articles I saw a schematic for a 175, one driver tube per channel.. pretty much the stock circuit with some streamlining. Does anyone have a working schematic that they can share?
 
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