B+ below 300v - any good? (aka can valve radios make good amp donors?)

[Loomer]

Got myself in a mini rabbit hole over the weekend spending some free time looking at valve radios listings and wondering if any could make for a great donor cabinet/chassis/transformers setup.

However when looking at the specs (or what I've been able to find, a LOT of service manuals are out there, but most of them have to be bought) it turns out that most of them run on very low B+ (about 240/250), at least from a guitar amp point of view) and sometimes output at weird (again, from a guitar standpoint) secondaries (like 3ohm, though I suspect hooking them up to a 4ohm speaker might not be the end of the world).

To cut a long story short, is there a track record of people using valve radios an convert them into amps? Can they make for good donors? And, conversely, are there any guitar amp circuits that could use the low B+ that many of those radios' PTs tap out?

Thanks!

[tubenit]

Take a look at 6BM8 tubes as a good candidate for lower B+ amp designs. 6BM8 tubes are still manufactured.


You will find numerous 6BM8 amp designs in a SCH format here:   
PC Express and JSchem - Schematics and Layout diagrams (el34world.com)

With respect, Tubenit

[kagliostro]

Also 6AQ5 &  6P1P are a choice

same tube as 6V6 only in a small envelope

Franco

[tubeswell]

EL84s are happy at 250V - a bit hungrier on the heaters than 6V6s

[bmccowan]

6CM6 is another 9 pin power tube that works very well in the 200-300 volt range. Its sound is similar to 6V6.
Also - not all will agree, but 6V6 tubes also sound good at 250 volts. Many old (1940s) 6V6 amps operated under 300v. I have a few and they sound great, but they do not do the modern high gain amp sound of course. I also have built 2x6V6 amps with VVR and they sound fine down in the 250 volt range.
Of course, its not all about voltage - the PT needs to satisfy the amperage demand.
OTs 3 ohms - no problem as you suspect.

[HotBluePlates]

... looking at valve radios listings and wondering if any could make for a great donor cabinet/chassis/transformers setup.

However ... it turns out that most of them run on very low B+ (about 240/250) ...

... are there any guitar amp circuits that could use the low B+ that many of those radios' PTs tap out

Whether these are "great donors" depends on your desired end-goal:

   -  If you want to build a "Fender ____" or a "Marshall ___," then save your money & buy parts made for the clone-amp market.

   -  If you intend to source/remove parts from the radios to re-use in some other amp build, then save your money and just buy the new, unused parts you need.

   -  If you're looking to build an amp louder than a Champ, tweed Princeton, Vox AC4, etc, then save your money and go buy the correct parts for a bigger amp.


I have not done any radio-to-amp conversions, but I've seen a lot of discussion on this board from others' attempts:
   -  Stripping out the RF and IF bits of the radio, and grafting on a suitable preamp can be a good path to a working guitar amp.
   -  There already is an audio section at the radio's output, and it's typically right-sized for moderate loudness at home.
   -  The power transformer, output transformer, and existing audio tube are already right-sized for each other.
   -  Keeping (almost) everything intact in the Audio & Power Supply sections (while replacing caps as-needed) is usually wise.
   -  Watch out for field-coil speakers, or keep the existing field-coil speaker (as it is integral to the power supply function).


I would not worry about "low voltages" at all for the preamp.
   -  We normally use high voltage because we need "high power output."
   -  The high power output requirement leads to Class AB, and large negative fixed-bias voltage in the power section.
   -  The large bias voltage means the phase inverter needs to deliver a large output signal.
   -  The "large signal" requirement means the power supply for the phase inverter needs a higher voltage.
   -  The rest of the preamp uses a higher supply voltage mainly out of convenience.

Given the points above, we might use a smaller supply voltage throughout a radio because:
   -  We don't need a big power output:  1-2 watts can be "very loud" and some players might wish for only 0.1w output.
   -  Small output power means small supply voltage, but also smaller bias voltage.
   -  Small bias voltage means a smaller drive signal from the preamp is adequate for full output power.
   -  Small power supply voltage in the preamp is acceptable because it supports the signal output needed.

I would try to reuse as much of the existing radio as possible, though I would understand the interest in using a different speaker.

[Loomer]

Thanks all for your input - very insightful and always picking up new knowledge, for which I'm very thankful!

Part of the allure for me is simply that it seems like a fun project and the radio itself would make for a fun cabinet. On the practical side, the fact you're getting a chassis as well as said cabinet plus potentially one transformer means that for the prices some go for (ie very little) it could be both a fun and worthwhile endeavour.

I've found a model for sale locally for about £30, which has a 250-0-250 PT and has a SE 6V6. While I totally get the point of "if you want a Fender xyz, get the parts for it", I can't help but think it could spawn a (vibro?) Champ-esque build or something along the lines of a Supro 1606/64 Super either with the 6V6 or one of the lesser voltage hungry alternatives listed above? Also all of the 6BM8 based suggestions made by Tubenit should fit the bill.

The OT may or may not be viable according to the secondary, which I don't think I'm mistaken in saying could be measured by putting a DMM across the speaker and see its resistance? Should it be pretty weird at least a 5w SE OT tends to be pretty cheap anyway (I can get one for £35/40), though I'd be fairly optimistic there as well. I should also mention that I'd definitely have a speaker out jack on it anyway and would not be contemplating using the speaker, though finding a suitable one that matches in size further down the line could be a nice touch. I'd most likely run it off the 10" in my AC4 (if the ohmage is a match) or, as I pretty much always end up doing when at home, through a dummy load and into IRs in Logic for easy recording and late night headphone playing.

Attached is the tubes spec for it off the service manual - I feel the current on tap might be low, but one power valve and one or two ECC83s for the front end/pre+tremolo shouldn't draw much more than what's already in use as per the service manual?

Again, I appreciate this is largely me going down a rabbit hole for the charm of it but please bear with me - after all, why are we here if not for some fun and a bit of tone and a sprinkling of learning on the side?! :)

[DummyLoad]

6F6, 6K6, 6EZ5, 12AB5, EL90, EL86, etc., EL86 is my favorite. Low B+ pair similar to EL84, makes 18W in P-P. with 250V B+


I built a few low cost SE amps with the EL86 and a couple of other "radio" tubes. They sound really nice pushed hard.


--Pete

[DummyLoad]

Almost forgot, 6BK5, but it's heater is hungry; 1.2A.


--Pete

[roarshock]

If you really like scooping out guts, desoldering, etc., and you like the look of an old tube radio, well, I'd suggest going for it, as long as you are willing to build what is within the confines of the PT and OT.  I've done a few conversions and before buying or picking up that next sweet old radio, record player, I'd suggest looking up the schematic and seeing if you can make it an amp that fits your needs/wants. Here's a few amps with less than 300v:
Silvertone 1333 (pp 6V6 @ 270 to the plates)
Silvertone  1472 (pp 6V6 @ 260 plates
Silvertone 1300 pp 6V6 @270 to plates:
Harmony H-200 (pp 6V6 @ 255v
Dano Century 30 265@ plates,
Dano Special 286@ plates,

Here's the one I keep playing then playing with: Its an old magnatone record player and radio combo that I chopped down to size and gutted everything but the PT and a few potentiometers before stuffing it with a Magnatone 210 (yes, it has the pitch shifting vibrato) plus added reverb, switchable bypass cap, and master volume.

[kagliostro]

Depending on the original input voltage of the radio and the line voltage you have, consider that those 250 - 0 - 250 will probably result in a bit higher voltage


Franco

[Loomer]

This is giving me hope! Found another candidate, attached are the voltage and current info from the service manual. About which, how would I go about establishing the total current the PT is tapping out? Would that be the full sum of the figures there? They all look pretty low to my untrained eye, but I suspect the fact they are different types of valves than we are used to see in guitar amps and are likely pushed a fair bit less has a something to do with it...

[Loomer]

Depending on the original input voltage of the radio and the line voltage you have, consider that those 250 - 0 - 250 will probably result in a bit higher voltage


Franco

That makes sense, especially using SS rectification. That said, I found a lot of them do have switchable primaries allowing to run between ~200 up to 250, which could go a decent way in addressing that, as while I’m aware that a few more volts would be fine if not a good thing I wonder whether the 6.3 supply might overshoot by a little more than it’s auspicabile?

[tubeswell]

how would I go about establishing the total current the PT is tapping out? Would that be the full sum of the figures there?

That table only gives current draw of each tube through the High Tension winding under idle (static) conditions. This is given by the cathode current for each tube type (because the total current in each tube goes through the cathode). For triodes, the cathode current is equal to the plate current (because the plate is passing the same amount of current out the other end). but for tetrodes of pentodes, the cathode current is the sum of the plate current and the screen current (because the current at the cathode gets split into 2 pathways (plate and screen) on its way through ‘the other end of’ the tube.
However, there are no figures given for the heater current draw for each tube, so you can’t finish the V.A. calculation for the PT by looking at that chart. You need to look up the respective tube data sheets.

[sluckey]

how would I go about establishing the total current the PT is tapping out? Would that be the full sum of the figures there?

You're in luck. The chart gives the total B+ current of 65.45mA. And for the filament current, go to TDSL Tube search and look up each tube filament current. Then just add it all up.

[Loomer]

how would I go about establishing the total current the PT is tapping out? Would that be the full sum of the figures there?

You're in luck. The chart gives the total B+ current of 65.45mA. And for the filament current, go to TDSL Tube search and look up each tube filament current. Then just add it all up.

And the grand total is 1.35A for the first one I posted and a whopping 3.45A for the second. Does this mean it's open season?

[sluckey]

It means that you know how much filament current the PT had to supply. Will it do more? Maybe. Maybe not. But it would be a safe if you don't exceed that number.

[Loomer]

It means that you know how much filament current the PT had to supply. Will it do more? Maybe. Maybe not. But it would be a safe if you don't exceed that number.

Correct - seen as I'd probably be looking at something Vibro Champ like I'd say I shouldn't trouble either limit :)

[sluckey]

I didn't see mention of a 5V winding on that PT. Not to worry. An EZ81 can handle 150mA and would easily power a Vibro Champ.

[Loomer]

I didn't see mention of a 5V winding on that PT. Not to worry. An EZ81 can handle 150mA and would easily power a Vibro Champ.

The first one I posted about has a 5Z4G rectifier and therefore a 5v winding (which partly also explains the lower 1.35A heaters draw), while the other comes with an EZ80 but was always catering for a generous 3.45A for the heaters. I guess in a VC the EZ80 would suffice without the need for an 81? I might even decide to go SS to eke out a few more volts (though I don't think the EZ's are that droppy?).

Also, in this SE landscape, I'm guessing from a practical stand point 6V6 or EL84 are basically interchangeable so long as current draw is within limits (which it would be in this case)?

[kagliostro]

Why to use a tube rectifier in an SE amp ?

The only reason I see is if you want to tame a bit B+

Franco

[Loomer]

Why to use a tube rectifier in an SE amp ?

The only reason I see is if you want to tame a bit B+

Franco

The only reason I might consider it is because it's already there! But might well switch to SS for long term ease of use and a little extra voltage to get me closer to 350 so yeah, I agree I'd be better off without :)

Grazie mille for your help!

[Loomer]

Well I have pulled the trigger and got myself the second one I posted about - single ended EL84. Will pick it up at some point in the coming week and start thinking about turning it into a silver face (Vibro) Champ, which should make good use of both transformers (assuming the OT hasn’t got some weird secondary).

More to come as I get my hands on it and begin to gut and rebuild...

[Loomer]

So the eagle has landed - took the radio home yesterday and it lives, which is a very good start! Another positive is that the speaker measured 4.2ohm across its lugs, which is handy. Unfortunately it's a weird 7" size speaker from what I can make out, so not easily replaced. Not the end of the world as I can use an external cabinet, but could have been neat to have a 6 or 8" guitar speaker in it! Saying that, a 6 might still be doable with a little adaptation...

The one thing that struck me is that the output transformer has 3 lugs on the primary, something I'd not seen on SE OTs. The schematic (attached) shows B+ connected to some kind of "centre tap" (which a CT it is not, but loosely using the term for illustrative purposes...!), then supplying both screen and the rest of the B+ supply rail. The schematic per se is good enough a starting point to go off of, which is good, but any insight as per how that transformer is wound and works would be really appreciated as it would give me a better understanding of what's going on there.

Power transformer is 250 CT (the other service manual I have quotes 258 at both of the EZ80's anodes, so technically a 258 - 0 - 258 or just measured with a hotter mains), with a 6.3v winding. I'll be looking to replace the EZ80 with diodes as this should take the voltage into the 300s, which should give a nice amount of juice to the circuit.

The amp has an EL84 output valve and despite the fact I'm looking at a champ-esque circuit I might decide to stick to it rather than go 6V6, for the simple reason that I already have the one it came with and more, too, but currently have no 6V6s on hand. Grid stopper is quite big at 10k, so might change that to a more conventional (at least looking at other EL84 SE circuits) 5k6. Cathode bypass are 180ohm and 50uF, so again, might stick to that (though I will probably swap the electro cap for a new one). Ultimately I'll probably be ripping it all out and starting mostly afresh as it looks to be a bit of a rats nest in there and most of the circuitry is redundant for my use. Chassis is very nice though, with plenty of sockets and space for a turret board.

An EF85 and ECC85 are also present in the circuit - my understanding is that the EF85 should be somewhat similar to what an ECC81 is to an 83 but for the EF86 of ye olde Vox fame, so could be interesting to experiment with further down the road. Same goes for the ECC85, which should be in the ballpark of being a lower gain ECC81, though I've not been able to find any feedback as per how either of them might perform in a guitar amp context. Probably two for the stash, at least for the time being.

Might drop the tremolo for simplicity's sake (and as sexy as tube tremolo is, I actually hardly ever use tremolo anyway), which would leave the four knobs at the front to act as Vol, Treble, Bass and On/Off. Should be neat and looking forward to getting going!

First step will be firing it back on and taking some measurements of voltages on the OT and at the rectifier.

[sluckey]

The one thing that struck me is that the output transformer has 3 lugs on the primary, something I'd not seen on SE OTs. The schematic (attached) shows B+ connected to some kind of "centre tap" (which a CT it is not, but loosely using the term for illustrative purposes...!), then supplying both screen and the rest of the B+ supply rail. The schematic per se is good enough a starting point to go off of, which is good, but any insight as per how that transformer is wound and works would be really appreciated as it would give me a better understanding of what's going on there.

That was fairly common back in the day. Part of the primary is simply being used as a choke for the rest of the amp.

[Loomer]

That was fairly common back in the day. Part of the primary is simply being used as a choke for the rest of the amp.

Ah, I had suspected that that's what was going on, but good to have a reliable confirmation rather than a hunch. Pretty neat system all in all!

[Loomer]

Took my DMM to the OT and we have 294v, which is very encouraging. I should expect this to exceed 300 were I to implement SS rectification, which would serve the EL84 very well.

That was the middle tap of the OT, the other one measured a couple v's less, which I assume is the post-choke feed. It'll be obvious once I take the chassis out anyway.

The voltage was down to 5 within seconds of switching it off - is this a sign of a set of ageing filter caps? I'm definitely going to swap those out anyway so not an issue but again, curious to learn and understand what I'm seeing a bit better!

[Williamblake]

The tubes do not get cold immediately and keep conducting.
I am very happy using parts from old radios, i use EL95, more than enough power at home.

[shooter]

could be, or with all the RF/IF extras you might just have "plenty" of paths to bleed down B+.  there might even be a bleed R, I didn't look to hard.

[Loomer]

Earmarked Sunday as a possible day 1 of the strip down of the guts.

One curiosity looking at the schematic (attached) - I saw the cathode bypass cap and resistor on the EL84 and assumed it was going to ground, but noticed they are actually going to the non-grounded side of the OT?! Is this a weird bias-cum-NF arrangement of sorts? Again, it will not survive the strip down anyway, but curious to understand what's going on and why.

Secondly, I'm looking at power filtering for the EL84-powered AA764 Champ which I will be building in it, factoring in that the OT includes a choke of sorts as confirmed above by Sluckey. Does the attached look good or should I allow for a series resistor post choke as per the radio schem? This as posted has an extra filter cap compared to the standard Champ circuit but then again, general consensus is that for reducing hum effectively adding one filter cap (rather than doubling the 20uF to 40 as some do suggest) is the way to go, so this would do as much...

[sluckey]

One curiosity looking at the schematic (attached) - I saw the cathode bypass cap and resistor on the EL84 and assumed it was going to ground, but noticed they are actually going to the non-grounded side of the OT?! Is this a weird bias-cum-NF arrangement of sorts?

Yes. That NFB circuit was popular back in the day.

[Loomer]

Yes. That NFB circuit was popular back in the day.

Interesting, thank you. What would it do to the end product compared to a regular cathode bias network and NFB circuit "as we know it" (ie resistor to before the power tube grid input as it is normally on guitar amps)?

Also, updated the above post with attachments which I'd originally forgotten...

[PRR]

I would leave that Fenman 90% stock, only fixing what is broke (and only the audio, not the RF/IF). Adapt guitar to the "PU" input and play hard, or add a LPB-like simple booster. Variations in NFB and filtering won't make huge differences, not like speaker and cabinet.

[scstill]

Take a look at 6BM8 tubes as a good candidate for lower B+ amp designs. 6BM8 tubes are still manufactured.
You will find numerous 6BM8 amp designs in a SCH format here:   
PC Express and JSchem - Schematics and Layout diagrams (el34world.com)
With respect, Tubenit

That is really clever with two tubes you get PushPull and PI
Sounds like it is worth the effort https://el34world.com/Forum/index.php?topic=6176.0
Why is it called HoSo56??

[Loomer]

I would leave that Fenman 90% stock, only fixing what is broke (and only the audio, not the RF/IF). Adapt guitar to the "PU" input and play hard, or add a LPB-like simple booster. Variations in NFB and filtering won't make huge differences, not like speaker and cabinet.

The fact it would need boosting in itself suggests to me some things about the stock circuit are broken from a guitar use standpoint, plus I'd like to have more options in terms of tone control (like the T+B AA764 controls, likely with a tone stack lift switch to tweed-ify it) and am not interested in keeping much authentic in it as it was bought more as a transformer donor, much like many in the US seem to look out for those Hammond organ amps.

I will be using it as a head, so that's the cabinet sorted, though it will be fun to kep the internal speaker and have it work as a stand alone, though I'm not holding much hope for its performance...!

[Loomer]

Started looking at the Champ guts for this - no AA764 Champ boards seem to be easily available or reasonably priced in the UK so been looking at a tagboard arrangement for this. It so happens that 18-lugs tagboards are readily available and I've managed to make full use of that...!

May I get some feedback on the attached layout? Going off the Fender schem and taking cues from the layout as available here in the library: https://el34world.com/charts/Schematics/files/Fender/Fender_champ_aa764_schem.pdf

It does however try to stick to the best practice approach of keeping preamp and power ground buses separate and makes use of the choke inbuilt in the OT as outlined a few posts above. I've drawn this layout for the 6V6 stock version (and has no tone stack bypass switch, which I'd place between ground and the 47k R off the Bass pot). Were I to go for the EL84 power section I'd stick to a schematic worked on and posted on another forum by Kley De Jong - the only differences I can spot are a different value cathode bypass cap on V2 and a screen grid resistor, which I could mount on the EL84 socket, meaning no layout differences as such.

Any input would be hugely appreciated as it's a first for me and can't help but feel there must be something that needs fixing...! :)

[sluckey]

I see several wiring errors and wrong component values. I suggest starting at the input jacks and compare to the original schematic and layout.

[PRR]

> I'd like to have more options in terms of

Make it work before you jazz it up.

I'll butt-out.

[HotBluePlates]

Why is it called HoSo56??

The original inspiration was the 65 Amps Soho.

[Loomer]

I see several wiring errors and wrong component values. I suggest starting at the input jacks and compare to the original schematic and layout.

Ah yes, definitely went trigger happy with the copy and paste and didn't amend values...! 😂 That's what you get for squishing it all into your lunch break at work :) How is the power/filtering side of things looking to you?

The gutting of the Fenman didn't quite happen this weekend but should be a good midweek evening activity 🤞 That should also allow for a corrected layout to form alongside

[Loomer]

Another lunch break, another spin with the layout - take 2 attached, which aims to correct the obvious wiring errors around the pots as well as amending those copy+paste related issues which resulted in incorrect values.

[sluckey]

47K on the bass pot should be 15K. 2.7K NFB resistor is connected to the wrong end of the 47Ω.

[sluckey]

Couple more issues...

All three pots are wired backwards.

V1 pin 8 bypass cap should be 2µF, not 25µF.

[Loomer]

Went through the trouble of inverting pots' connections and now you just made it obvious that I was reading them upside down, therefore back to front...! 😂

Thank you for all the spots, will amend and go through again.

I've removed the chassis from the cabinet and figuring out which lug of what transformer does what, thankfully it's all pretty straight forward. There are two 6.3v bulbs behind what was the frequency panel which are going to make for a really nice glorified pilot light!

The amp has some values in terms of caps and resistors which I can use for my own amp - is it worth recycling or best to go metal film etc since the expense is such a drop in the ocean all in all? And does the bad rep for old caps only apply to electros or is it a general rule that they will eventually wane and need replacing?

It's an absolute rat's nest in there so keen to clear it off but want to make sure I don't damage anything that can be saved/might be worth saving, be it for my own use or perhaps some radio enthusiast that might need bits for a restauration.

[sluckey]

I'm not fond of reusing resistors and caps.

[scstill]

I love building old tube radios that cannot be salvaged into guitar amps.
My initial inspiration has been "Squareamps"  see on instagram

Here is one I did called "Brownie" a Champ with a master volume and 8"WGS.
Original rats nest, gutted and completed chassis Pics

Can see progression at link below.
Cert is outdated but safe to click through to it.
My son is admin and has been putting me off :-(
https://stillampd.com/philco-champ

[Loomer]

I love building old tube radios that cannot be salvaged into guitar amps.
My initial inspiration has been "Squareamps"  see on instagram

Here is one I did called "Brownie" a Champ with a master volume and 8"WGS.
Original rats nest, gutted and completed chassis Pics

Can see progression at link below.
Cert is outdated but safe to click through to it.
My son is admin and has been putting me off :-(
https://stillampd.com/philco-champ

If my end result will look half as clean and tidy as that I'll be a very happy man! For now here's the rats nest I'm looking at.

Do you use anything specific to clean the chassis and/or any pins/contacts of parts you may be repurposing? Though I'm not holding too much hope of being able to, I liked the idea of being able to reuse the sockets, but some are pretty guncked up to the point they struggle to beep for continuity sometimes. Same goes for the transformers' pins and I'm definitely repurposing those.

I'm currently tracing and labelling all the transformer pins and beyond that I don't think I'll be repurposing too much - the tone pot also clicks the radio on and off and might reuse it as a simple on/off switch. I've labelled one tap off the OT as "Choke B+ out" which I'm sure is a misnomer but makes sense (at least to me) in the context of this OT having it's little internal choke old school style. Not encountered it before so not sure what I should call it...!

Also slightly puzzled at the PT - doesn't it have one more ground connection than it "should"? Also, the radio worked fine but now if I click the on/off pot on the red and black coming from the IEC are shorted, and the tap I labelled "on/off sw gnd" is also shorted to the primary input (which right now is going into the 225-250 tap). Am I misreading this or is something off?

There is one cap (bottom centre right in the photo) which is clearly pretty new and has long leads so might give that a new life - it's a 47n which fits perfectly in the tonestack.

The heater supply currently has one end to ground (along with the CT) and the other's the 6.3v - admittedly the heaters part of the power supply is one bit I've largely ignored and took for granted, but my feeling was that there were not directly grounded? Or does that simply depend on the transformer and this one clearly calls for direct grounding at the star?

[shooter]

doing much the same as scstill, gut, clean, think, steal, draw, begin...
 https://el34world.com/Forum/index.php?topic=29332.msg327032#msg327032


in a single evening with your favorite single malt, a blunt, music, whatever gets you in the groove, by lights out you've gutted it and hanging it to drain. 2 days later it's cleaned up ready for primer, 2 weeks later you have a working schematic, layout, parts list, milk the cash cow, walla, a new beginning.

[scstill]

I love the gutting part, strangely satisfying.
If the radio has transformers or pre-octal sockets, I re-use those.
I leave the chassis as patina'd as I find it.  (check out "PhuelCel8" for a twist on the chassis)
I try to leave as much of the radio provenance as possible.
I always use the original knobs or source same if missing.
I always stuff the biggest guitar speaker as possible and fabricate a new baffle.
If there is a back I cut a tasteful hole for cooling.
Tubes from a battery radio (like Brownie) are not reusable for AC based designs
But from an AC radio, Power and rectifier tubes are often reusable.
Other tubes will be remote cutoff so I find Sharp cutoff equivalent
For some strange reason I can never throw any of the old guts away.
Thinking it might come in "handy" some day. In reality its not usually useful.

[sluckey]

Those wafer style sockets are not worth trying to salvage.